| Ahoy! This here is the 1st Featured Article.
"Monkey D. Luffy" has been featured, meaning it was chosen as an article of interest.
As captain of the Straw Hat Pirates, Monkey D. Luffy has immense physical strength, and is capable of lifting up large boulders, breaking stone, shattering steel with his bare hands, pushing apart large buildings and shoulder flipping a huge man; his strength was further proven when he effortlessly stopped a stomp from Donquixote Doflamingo, a tremendously strong man who is twice Luffy's size, with only one foot from an angle with no leverage. Additionally, Luffy has always fought the strongest villain of the story arc (except in the Romance Dawn Arc). Luffy's sheer physical strength and immense dexterity is a result of his grandfather's unorthodox training methods (such as being thrown into a bottomless ravine, tied to a balloon, thrown into a forest at night, etc.) and he claimed he had a punch as powerful as a pistol even at seven years of age. His endurance and durability is incredible; taking continuous, deadly assaults from powerful opponents that would have killed a normal person easily in most of his fights, yet still being able to stand up and continue fighting effectively.
Luffy also possesses tremendous speed, agility, and reflexes to match his strength and endurance. In fact, on more than one occasion, Luffy was able to anticipate moves and counter attacks that would normally be beyond his field of vision due to his extremely sharp reflexes. He is also shown to increase in strength quite dramatically in a short period of time, most noticeably being the fight against Minotaurus, where the first time it took the combined efforts of Mr. 2, Mr. 3, and Buggy just to beat him, but the next time, Luffy defeated him with a single "Gomu Gomu no Jet Pistol".
His vast strength is only exceeded by his enormous willpower, as demonstrated on several occasions throughout the series, most noted of all in the Thriller Bark Arc when he manages to take in 100 shadows without passing out, compared to normal humans, who can only take in 2 or 3. This willpower even lets him survive far beyond what normal people are capable of, as demonstrated when he was poisoned very far beyond what a human is capable of surviving, only living on despite his critical condition through sheer willpower. This is also shown when he survives through Emporio Ivankov's "Healing Hormones" ability, which even with a slim chance of surviving had not only survived the endeavor, but made a recovery in twenty hours when the normal time for the healing procedure is two days. This was later shown with Basil Hawkins' "fortune telling" ability, as despite doing it multiple times, he could never get Luffy's chances of survival to reach 0.
He also possesses extraordinary jaw strength, as seen in the Orange Town Arc in the manga, where he had almost chewed through the metal bars of the cage Buggy put him in. In the following arc, he shattered Jango's steel chakram with his teeth alone (anime). He also ate the cage that Gekko Moriah put him in, and managed to give Rob Lucci a small bite wound, as well as break the steel chain used to bind Nami (in Franky's body) after the timeskip. His greatest feat in this area, however, was that he managed to make Jinbe, who is known to have an extremely high tolerance towards pain, yell out in pain when he bit the fishman's arm.
Luffy is also shown to be extremely agile. Early on in the series, Luffy is seen being able to react to foes faster than him, like Kuro, Arlong, Bellamy, and Enel. After learning the CP9's Soru technique to enhance both speed and strength, he became even more so. After the timeskip he has become even faster, being able to dodge attacks even while in Gear Third, and even creating enough friction while running at full speed to set the ground on fire.
Luffy's fighting style consists of adept hand-to-hand combat, supplemented with his physical prowess and the abilities of the Gomu Gomu no Mi. Such skill allows him to hold his own against combat specialists like Rob Lucci. Unlike Zoro or Sanji, Luffy's fighting style is completely improvised self taught; it follows no particular code of honor, and so if necessary, he will attack women or animals, hit below the belt, attack his enemies even if they have their backs turned or are otherwise unprepared or unsuspecting, use enemies as human shields and even bite his opponents. While fighting, Luffy has been shown to be highly adept at improvising, and regularly comes up with creative counterattacks and unusual techniques to use against his enemies. This however leads both enemies and allies alike to wonder if Luffy is taking the fight seriously, especially when he comes up with ridiculous and over the top moves (like Crocodile when Luffy became Mizu Luffy), which prompts Luffy to respond that he's always serious.
When Luffy fights, he relies heavily on his instincts, which, interestingly enough, are mostly correct. Even as early as the Arlong Park Arc, after getting bitten he managed to escape with his arm still in one piece by slamming Arlong's head to loosen his jaw to get it out instead of simply pulling it. He picked out the real Mr. 3 from a bunch of wax look-a-likes on a hunch. He also destroyed Enel's "Raigo" using the gold ball as a conductor, but according to Oda he had no real idea what he was doing and was acting out of instinct. Before even learning Kenbunshoku Haki, Luffy could easily dodge any attack by relying on his instinct as shown in his battle against Enel and Rob Lucci.
During his childhood, Luffy seems to have at least become competent with a staff, as he is seen using one against a variety of opponents.
He also appears to be intelligent enough to at least understand fundamental concepts, such as rubber being a natural insulator, which might be why he did not bother ducking out of the way of Enel's lightning attacks as it would have been pointless because of his immunity. He also was able to develop new techniques such as "Gear Second" and "Gear Third", using logical concepts and knowledge of rubber and its properties. While easily noticeable as the least strategic member of his own crew, largely due to his tendency to simply barge in head-first into battle (often without any kind of battle plan or even any knowledge of his opponent's abilities), Luffy is a highly adaptive combatant. He is constantly coming up with ways to keep ahead of his foes, either by taking advantage of his own strength and Devil Fruit powers or utilizing the opponent's own strengths (along with their weaknesses) against them. This causes even warriors long considered unbeatable to have trouble keeping up. Also, even if most of the time he acts instinctively, in some cases Luffy has shown to be intelligent enough to give some orders to his crewmates in the wake of making a strategy or simply making things go as he prefers. This usually ends up being an advantage for the crew.
After the timeskip, Luffy has demonstrated more intelligence during the heat of battle, as he was able to use Trafalgar Law's powers to his advantage and even fool a Shichibukai as cunning as Doflamingo into being swapped out so Luffy could land a blow on him.
Miscellaneous Skills and WeaknessesEdit
He is heavily susceptible to any form of hypnotism and does not have the sense to turn away, such as Jango's powers of hypnosis or Miss Goldenweek's Colors Trap. He is also easily distracted when he sees something that's "just too cool", like seeing Chopper's transformations for the first time, the Thousand Sunny's Gaon Cannon, an energy beam from a Pacifista, his wax armor made from Mr.3's Doru Doru no Mi powers, or the Iron Pirate "Franky Shogun", ignoring everything around him.
Luffy also has the mysterious and uncanny ability to, while completely asleep, eat as if he were awake, and even knows when more food has been placed on the table. This is probably purely based on muscle memory since what Luffy does best is fighting and eating. It's been shown on several occasions that meat may act as more of a power source than simply a favorite food for Luffy, as whenever he becomes exhausted or tired from a fierce battle, he simply eats some meat and he's back in fighting condition again.
Another running gag in the series is Luffy's inability to draw. At the start of the Arlong Park Arc, imagining how a fishman would look, Luffy drew a fish with tentacle-like paws and an anthropomorphic fish with arms, legs and hair (greatly incensing Sanji, who erroneously thought that Nami could be a mermaid and thus mistakenly believed that Luffy was drawing her ugly). Before the Straw Hats arrived at Water 7, Luffy drew a childish picture of what he wanted the future shipwright to look like (coincidentally, it resembled Franky). This inability also extends to Jolly Rogers; the first Jolly Roger of the Straw Hat Pirates was a bad drawing designed by Luffy himself (he later used a similarly bad drawn version of his Jolly Roger as a promise marker on the face of Laboon) while also drawing a bad version of Foxy's flag after taking it from him in the Long Ring Long Land Arc.
Another of Luffy's gags is his inability to do chores. Luffy is a disaster when it comes to doing simple errands, as shown when he was a chore boy in Baratie. Everything he tried to do or help with only ended up worse. It got to the point where Zeff gladly allowed him to go after defeating Don Krieg, claiming the damage Luffy could inflict if he stays would probably put his restaurant out of business. Even a simple errand like purchasing water ends up with him being chased by the Marines. In fact, it has come to the point where Luffy has to have a chaperone even if he is only going to explore so as not to cause trouble, or do anything stupid, and even then it is not guaranteed that he will not.
Several of Luffy's feats of greatness are related to food. When food was involved, he was able to instantly calculate the amount of meals he missed while sleeping for 3 day after his fight with Crocodile. Since Luffy hated missing meals, he developed a skill that allowed him to eat while sleeping, which was first shown after the incident at Enies Lobby. After being poisoned by Magellan and surviving Emporio Ivankov's healing hormone, Luffy was left in an incredibly emaciated state where he was just skin and bones, but was able to eat several days' worth of food and instantly return to normal size with his muscle mass restored, similar to the Life Return: Shoka, Kyushi technique used by CP9 member Kumadori.
Even though Luffy is a sailor and the captain of his ship, he has no sense of direction. He believes that if one is to go north, he has to head in a "cold-ish" direction. As a result of this, coupled with his ability to get stuck in certain situations, he tends to arrive barely in time to fight his opponent.
One of Luffy's greatest advantages is that people actually tend to underestimate him. Either due to his bounty, his actions, or their own arrogance, his opponents usually take him lightly before discovering Luffy's great strength and determination. Because he is underestimated, his opponents (including the Shichibukai) tend to let their guards down, allowing Luffy to gradually learn and adapt his fighting style accordingly. However, after the global revelation of his heritage and his actions, this advantage fades away, as people takes his threat seriously based on the third-hand information.
A second advantage is his unpredictability. Due to his unique, fun-loving, battle-ready personality, and his elastic physique, opponents (and even his allies) are caught off guard by his tactics. This trait has given people the impression of him being reckless, if not insane and keeps people second guessing.
Though it's never been stated, Luffy seems to be able to hear the voices of creatures. During the Warship Island Arc, he claims to sort of hear the voice of Ryu the dragon (though, this is non-canon). It is mentioned a second time during the Fishman Island Arc when the Sea Kings come to save Noah. One of them thinks Luffy hears their voice, causing them to think back to a young Gol D. Roger, who also heard them in his journey in the depths of the sea. Additionally, Luffy – along with Kozuki Momonosuke – was one of the only two people on Zou able to hear the calling voice of the elephant Zunisha, while it was being attacked by Jack. Pedro further affirmed that this ability of hearing the Voice of All Things was shared by Gol D. Roger and Kozuki Oden.
Though not a skill or ability, Luffy is said to have incredible luck. His luck is so great that people around him, like Smoker, Ivankov, Elder Nyon, and even his own crew think that they were miracles, or even divine intervention, though in most cases it has to do with his incredible willpower. Examples are:
- Surviving the execution done by Buggy  and managing to escape the Marines in Loguetown thanks to a freak storm.
- Surviving two defeats by Crocodile, the second one being incredibly lucky because the desperate water blast he spat upwards as Mizu Luffy when Crocodile grabbed him by the throat (which Crocodile dodged before drying Luffy's body with his Suna Suna no Mi powers) eventually landed back and rehydrated him to save his life.
- Picking out a dud in a basket full of exploding apples;
- Defeating Rob Lucci in battle, through both sheer willpower and his unbelievable endurance. 
- Managing to beat Gekko Moriah just before the sun rises, making him cough up all the shadows he stole in time.
- Accidentally making the man-hating Boa Hancock fall in love with him;
- Having the willpower to survive Magellan's poison and recover from it through pure strength of will and some hormone enhancement, when it was said there was not even a shred of hope that he would survive, and that even antidotes were out of the question.
- Participating in the Battle of Marineford and surviving.
- Being poisoned by Hyouzou only to discover he developed strong resistances to even the deadliest of poisons due to his fight with Magellan.
- Defeating Donquixote Doflamingo before the Birdcage kills everyone, with his victory being very lucky as after his Gear Fourth wore off, he needed ten minutes to regain his Haki and had not several gladiators held off Doflamingo and the Birdcage then Luffy would have never defeated him.
However, Luffy's luck has not always held, most notably when he is using Gears. When using Gear Third for the first time against Rob Lucci, Luffy failed to defeat him before Gear Third ended, and Lucci was able to take advantage of his weakened form to do major damage and would have been kill by him if not for Luffy manage to fracture his leg with Gear Third. The same thing happened when using Gear Fourth for the first time against Donquixote Doflamingo, but the aftereffects were longer, leaving it up to several gladiators to protect him from certain death.
According to Dracule Mihawk, Luffy has the most dangerous ability in the world: that of turning anyone around him into his ally, including former enemies. Luffy's charisma has earned him many powerful friends and allies in times of need, allowing him to escape the tightest situations. In a conversation between Ace and Vivi, it is shown that Ace is somewhat aware of this ability, as he mentions that Luffy has a strange charm that causes people to gather around him. In fact his charm is great enough that he earned the respect of Whitebeard after talking with him for a few seconds and later on he earned his complete faith to save Ace as Whitebeard ordered his crew and allies to back up Luffy. He was also able to make Chinjao, a man who hated his grandfather for thirty years and extended his hatred to his descentants, an ally that is willing to have his grandsons Happo Navy work for him because he restored his head to its old shape. In fact, this ability has saved him on several occasions, when any plan or his own personal strength has failed, gathering unlikely allies in his moment of need.
During the two-year absence, with his bounty raised, he earned an infamous reputation which was taken advantage of by Demaro Black to bring fear to the hearts of people in Saboady Archipelago as well as recruit powerful members. His reputation is high enough to be noted by New World Pirates, as some were shocked when they found out that Caesar had captured him. During the Corrida Colosseum tournament in Dressrosa, several contestants express fear over his presence, even Bartolomeo who had casually won the B Block.
After the timeskip, Luffy has grown immensely in power and skill. He has shown new mastery over his Gear Second and Gear Third along with his Haki, and easily destroyed a Pacifista with a single punch in conjunction with his Gear Second and Busoshoku Haki (a feat which has been shown to be amazingly difficult). Later, he defeated the Kraken with one hit from Gear Third imbued with Haki in a similar manner, and then managed to beat Vander Decken IX while tied up. Another testament to his power was shown when he defeated Hody Jones while fighting underwater for the majority of the fight, and only received one bite wound throughout the whole duration. He is strong enough to be able to destroy Noah, a ship half the size of Fishman Island, while suffering from blood loss and (as noted by the Sea Kings) would have done so if they didn't show up in time, as well as being able to defeat Don Chinjao, a pirate worth over 500,000,000 who once fought against Garp. He has also grown to be much more durable, as the same attack from Caesar Clown that caused heavy damage to Sanji's body did not leave any lasting injuries on Luffy. While initially stunned by the attack, he appeared completely uninjured almost immediately afterwards. While the Straw Hats were on their way to Fishman Island, he showed no discomfort in the range of temperatures given, hot or cold.
He has also gained powerful antitoxins in his blood stream from his fight with Magellan in Impel Down, which grant him a high resistance against poison. Hyouzou, a poisonous blue-ringed octopus merman of the New Fishman Pirates, poisoned Luffy during their fight and Luffy would not have taken any notice, if Chopper had not seen the entry point in his arm. The blue-ringed octopus possesses one of the real world's deadliest poisons and the fact that Luffy could shrug it off like it was nothing is a testament to the strength of his immune system. He is also able to counter against Caesar's own poisonous gases. He is able to completely resist the H2S (a gas that petrified people with a touch) in Caesar's enhanced form without any sign of being poisoned. However,extremely powerful poison normally capable of instant death may still be able to incapacitate him.
Like all Devil Fruit users, Luffy cannot swim. However, unlike other Devil Fruit users, he does not avoid water sports, and sometimes will jump into the ocean to save someone from drowning (though will drown himself as well). Before eating his Devil Fruit, Luffy didn't know how to swim anyway, so this has made little difference in this capacity. At the time Shanks visited Luffy's hometown, Luffy had decided he would learn how to swim by the time Shanks left so that he could leave with them, indicating Luffy had yet to learn how to swim. He does seem to know that a person cannot eat more than one Devil Fruit, as shown when he said he couldn't eat the Mera Mera no Mi.
Another one of Luffy's amazing skills is his capability to tame and/or befriend creatures in a very short amount of time. Several examples are:
- During the Drum Island Arc, after saving the life of a parent Lapahn that was buried underneath the snow from the avalanche they caused, the Lapahns repaid the favor by holding off Wapol and his minions Chess and Kuromarimo for as long as they could so Luffy could get up the mountain.
- During the Alabasta Arc, he was able to befriend the Kung-Fu Dugongs.
- During the Thriller Bark Arc, he was able to tame the Cerberus.
- Prior to the Return to Sabaody Arc, he was able to tame all the animals on Rusukaina.
- During the Fishman Island Arc, he was able to tame and name the Kraken (Surume).
- During the fight at Corrida Colosseum, he was able to tame and name the Fighting Bull (Ucy).
However, despite his immense strength, one of his greatest weaknesses (and sometimes strength) is that Luffy's strength is heavily influenced by his mental state and willpower. If Luffy has a clear goal and is reinforced with confidence, his strength is unimaginable, capable of splitting towns and wiping out opponents with ease using pure brute force. However, if his confidence is shaken, and he is unsure of what is going on, Luffy strength is severely affected, and is incapable of putting a true fight. This is best displayed between his first and second battle with Rob Lucci. During his first fight at Water 7, Luffy, being unsure of the circumstances, and met with Robin's refusal, was barely able to do anything, even against an untransformed Lucci, let alone Blueno. But during their second round in Ennies Lobby, after gaining a full understanding of the circumstances, and reaffirming his resolve, Luffy was capable of giving a Lucci a run for his money even before activating his new Gears.
While Luffy enjoys eating large sums of food, he is terrible in handling and preparing it. His extreme appetite led him to constantly steal food from the fridge prior to the installed lock on the Thousand Sunny, leading to heavy depletion of provisions for extended sailing. He has no culinary skills, as when he created his "Random Curry", he squandered the ship's entire week's worth of rations due to repeated mistakes, and the end results was a huge pot of inedible substance that led the people on board to starve as a result,. Ultimately this led to Nami to take over with the cooking and she viciously made it clear that he was never to help out in the kitchen again. 
- Further information: Gomu Gomu no Mi
Luffy gained extraordinary stretching powers from eating the Gomu Gomu no Mi (lit. Rubber Rubber Fruit, Gum-Gum Fruit in the English dub), which is one of the rare and legendary Devil Fruits. After consuming the Gomu Gomu no Mi, Luffy's body became like rubber, giving him the ability to stretch and attack long distances.
Having undergone intense training for over ten years, Luffy is now able to supplement his stretching powers with immense strength, agility, and creativity in combat. His fighting style is largely improvised, and thus relies heavily on his Devil Fruit powers. It should also be noted that Luffy cannot automatically stretch his limbs out (like superheroes with stretching powers, (i.e: Mr. Fantastic or Plastic Man), and since his body acts much like an actual rubber band, he has to throw some force into his punches in order for his limbs to stretch out. It should be noted that he has somehow managed to do it automatically (much like the aforementioned superheroes) after the timeskip. However, he has been shown to be able to hold his limbs outstretched for a long period of time, as seen when he reaches his arm out about half a mile down to try and retrieve Usopp from falling through the Sea Clouds.
Luffy regularly uses his stretching powers in ingenious and creative ways, as he is able to use the malleable stretchiness and elasticity of his limbs to gain tremendous velocity, and hit his enemies with devastating impacts and blows. His rubber body is also extremely durable and virtually immune to blunt attacks such as bullets (in One Piece, bullets are still round pellets, except for Don Krieg's), punches, and electricity, more often than not, bouncing off his body harmlessly or canceling out the attack. It has even become a running gag that people find out the hard way that Luffy is made of rubber when they shoot at him, only to have the bullets bounce back at them.
Another running gag is that whenever Luffy's body is in a dangerous situation that would kill a normal person, he simply states that "he's made of rubber, so it's okay", or acts like it is a small problem despite that person trying to kill him, such as being shot in the heart. However, he is still normally susceptible to sharp objects such as swords and knives as well as nonphysical attacks like heat, cold, dehydration, and poison (though after the timeskip, Luffy has been shown a strong immunity to poison due to his fight against Magellan in Impel Down). Not only can he use his stretchiness to increase the range and strength of his attacks, but on some rare occasions he can also use his stretched limbs to help restrain and even control weaker foes like puppets (to fight for him).
By taking advantage of the unique physical abilities granted by his Devil Fruit, Luffy has invented techniques that augment his speed and strength in different ways, though each one also has corresponding physical drawbacks. He refers to these techniques as Gears.
- Further information: Gomu Gomu no Mi/Gear Second Techniques
Gear Second (ギア･セカンド Gia Sekando?) is where Luffy uses his legs to pump blood throughout his body at a much faster rate. Activating Gear Second also uses a lot of stored energy from his body. Leaving his body exhausted, his heart rate also increases to levels that are normally impossible. His veins are able to withstand this since they are made of rubber, thanks to the Gomu Gomu no Mi. In this form, Luffy gains a considerable boost in speed and strength.
During the Enies Lobby Arc, Rob Lucci mentions that this ability is similar to steroids because his muscles are receiving enough blood to do things otherwise impossible. Rob Lucci also noted that Gear Second does damage to Luffy's own body and in turn drastically reduces his stamina and his lifespan begins to diminish due to prolonged use.
Luffy first discovers this Gear unofficially in the 7th One Piece Movie, where he has a large mechanical arm falling on him, he catches it, and the impact exerts extreme force on Luffy's legs, causing him to unintentionally pump blood at an accelerated rate to perform Gear Second and use the "Gomu Gomu no Jet Bazooka" (though he simply refers to is as a normal "Gomu Gomu no Bazooka") to defeat a giant robotic battlesuit.
After the timeskip, it appears that Luffy has gained enough control over his Gear Second form, that he is able to use it in a single limb rather than his whole body. This, in conjunction with his Busoshoku Haki, was able to take out a Pacifista with a single punch, something that took the entire Straw Hat crew to do before the timeskip. His strength in this form has also increased to the point where he could knock over a large creature like Wadatsumi with a single "Gomu Gomu no Jet Pistol", breaking one of the giant fishman's teeth. Luffy can use Busoshoku Haki combined with Gear Second to perform "Gomu Gomu no Red Hawk", which causes his fist to ignite into flames. It seems that Luffy has become far more adept with this gear as he has been using Gear Second attacks much more frequently than before the timeskip.
- Further information: Gomu Gomu no Mi/Gear Third Techniques
Gear Third (ギア･サード Gia Sādo?) is where Luffy pumps air through his bones to make them literally gigantic. Obviously, only Luffy can do such a thing by using the Gomu Gomu no Mi. Used with his already-strong physiology, this apparently gives his arm more mass and a larger area to attack with far greater force, but he sacrifices mobility for this strength, as his limbs are now so large that Luffy has extreme trouble moving unless he is in his Fusen form.
Another after effect of this is that Luffy is reduced to child-sized proportions, the duration of which is equal to the time he spent in Gear Third. Also, he is able to use both gears at the same time which he uses to defeat Gekko Moriah. The Gear Third technique is first hinted at during Luffy's fight with Blueno, and first used, but not shown when Luffy is chasing Rob Lucci and Spandam, but is not seen until a later battle with Rob Lucci.
After the timeskip, Luffy's Gear Third is vastly improved upon. Previously, Gear Third would increase the size of the majority of Luffy's arm, thus reducing the speed of the attack in exchange for a powerful impact. However post-timeskip Luffy can seemingly control where the air is allowed to "sit" within his limbs, where his fist becomes large but allows a large mass to form behind the fist as the equivalent of the mass he would have achieved having his arm fully inflated. This allows a majority of Luffy's arm to remain as it is, allowing him to stretch it, thus allowing him to attack much faster than before the two-year absence.
Luffy is also shown capable of using Gear Third at the same time as Busoshoku Haki, causing his arm to turn black and harden, with his arm in the ocean (which would normally drain a Devil Fruit user of their power). While he is still affected by the ocean, he lands a punch which knocks an attacking Kraken out on the way to Fishman Island. Luffy is confirmed to have overcome his weakness of shrinking when deactivating this Gear, after inflating both his arms and using "Gomu Gomu no Elephant Gatling" on Noah for a prolonged period of time and not turning into his chibi form.
- When Luffy reverts to his chibi form, his clothes, including his straw hat, change relative to his actual size. When Luffy moves his mass throughout his body, however, his clothes remain the same size. This appears to be the same throughout every one of Luffy's mass increases, per example his "Nightmare Luffy" form.
- Further information: Gomu Gomu no Mi/Gear Fourth Techniques
Gear Fourth (ギア4フォース Gia Fōsu) is a technique which Luffy developed during the time skip when he fought giant creatures on Rusukaina. He first coats his arm in Busoshoku Haki and then bites into his forearm. Similar to how he activates Gear Third, he blows an incredible amount of air into his body, but this time he inflates his muscular structure.
In this form, his body's proportions become warped and is much larger in size, with his arms, upper torso, and legs coated in Busoshoku Haki. The coating across his torso resemble the wispy ends made from flames, and he also gains shading around the inner and outer edges of his eyes.
As a side-effect he is incapable of standing still on the ground, and instead constantly bounces on the spot. His physical strength and speed are increased to the point where he is able to overwhelm Donquixote Doflamingo, whereas beforehand both Gear Second and Gear Third were ineffective in the fight.
It also shows a versatile side of the Gomu Gomu no Mi when using the elasticity to achieve a form of pseudo-flight and changing the direction of his attacks mid-strike to hit a moving opponent, strengthening his attacks in a similar manner to the Bane Bane no Mi by compressing his arms and legs like springs. This form, much like Gear Second, seems to utilize the principles of Rokushiki. It possesses both high speed movement reminiscent of Soru and the ability to kick off the air, similar to Geppo, creatively adapted to work even better with his body's elasticity, not just bouncing off the air but allowing punches and attacks to bounce off his own body.
According to Doflamingo, the power of his attacks increases greatly in this form. His durability is also vastly enhanced, as despite being his body being rubber and coated in Busoshoku Haki, as a result Doflamingo's immensely strong kicks simply bounce off of his body.
Another side-effect is its limit to how long Luffy can keep Gear Fourth active, as noted by both Luffy himself and Doflamingo. Once Gear Fourth reaches the limit, it automatically deactivates and Luffy is left exhausted, barely able to move as Haki originates from the user's life force. He is also left unable to use Haki for ten minutes after using this technique. Even afterwards, Gear Fourth is extremely taxing on Luffy's body and stamina; after regaining his Haki from using Gear Fourth once, he barely had enough strength left to fight back, and using it briefly for a second time shortly after rendered him unconscious.
- Further information: Haki
Shortly before the two year time skip, Luffy had awakened the ability known as "Haki" and is one of the few known people able to use all three types. Luffy was identified to possess this mysterious ability by Blackbeard after their first encounter in Jaya. He first showed the ability to use it when he knocked out Duval's steed, Motobaro, without actually hitting him. Since then, he showed increased but irregular usage of it, with very little to no control, as the series went on. It was only after the Battle of Marineford, when he started training with Silvers Rayleigh, that he actually learned about Haki and how to control it. Though it was stated that 2 years was too short a time to learn the basics of Haki, Luffy has shown a natural affinity for it, learning it in 18 months. Since reuniting with his crew Luffy has been shown to consciously, actively, and easily use Haki in combat.
After Ace was sent away to the Marine Headquarters, Luffy decided to break out of Impel Down and head for Marineford. In the process, he ran into an intruding Blackbeard who noted that Luffy's Haki increased since last time they met (in Jaya). It could be speculated that Blackbeard already noticed Luffy's Haki possession since their first meeting. The fourth time Luffy released his Haki was at Marineford, when he saw Ace about to be executed. It was then that Ace and the Marines learned of his possession of Haki, and of the Haoshoku type to top it off. This made him even more threatening to the government, although he was already threatening enough without it.
After the Marineford War, Luffy decided to train with Rayleigh. Luffy managed to learn the basics of Haki within a year and a half, even though Rayleigh had intended to spend the entire two years teaching him, meaning that he was either a fast learner once he understood the concept, or he has an innate affinity for Haki. Rayleigh departed after a year and a half, leaving Luffy to train by himself for the remaining six months. It should be noted that Luffy possesses what is considered to be a large amount of Haki.
Luffy is able to use Haoshoku Haki, a type of Haki possessed only by one in a million people. Luffy used this ability several times in the series, as it was the type of Haki that manifested the earliest.
The first time Luffy was identified to have possessed this type of Haki was when he stopped Boa Sandersonia from smashing a petrified Marguerite, although he first showed possession of this type of Haki when he scared off Duval's bison steed, Motobaro.
When he protected Bentham from being attacked by wolves back at Impel Down (Level 5) Luffy released his Haki unconsciously. During the war at Marineford, he also used another burst of Haoshoku Haki when he saw Ace about to be executed, which knocked out a lot of individuals, both Marines and Pirates. This made it clear that Luffy, setting aside his identity as the revolutionary Dragon's son, is also a serious threat as a pirate just by possessing Haoshoku Haki.
Before training under Rayleigh, Luffy displayed limited to no control over this ability, and did not seem to realize he had it, but used it on instinct whenever it seemed to be most needed, and could still use it even when extremely injured.
With this training, Luffy has demonstrated the ability to focus his Haoshoku Haki, knocking out a small group with a quick glare without affecting anyone else. A possibility of Luffy's Haoshoku Haki is that he can tame large animals as he was capable of taming all the animals of Rusukaina Island, and tame the Kraken, which he did with great success in a very short time. Up until the fight with the New Fishman Pirates, Luffy has only used Haoshoku Haki when he needs to get people out of the way with minimum damage. The true extent of Luffy's Haki is seen when he knocks out 50,000 of Hody Jones' men. During his fight with Chinjao during the Corrida Colosseum tournament, the two unleashed a powerful wave of Haoshoku Haki when they clashed fists. This Haki has become Luffy's specialty.
Since training with Silvers Rayleigh, Luffy appears to have gained significant proficiency in Kenbunshoku Haki, allowing him to tell what an opponent intends to do. He was able to effortlessly dodge a bullet shot at point-blank range by Demaro Black as well as laser projectiles fired by a Pacifista, commenting that the last attack was "slow". His proficiency with this skill is truly shown when he was able to completely avoid Hody Jones' Yabusame without effort. Luffy also displayed being able to discern Caribou's presence within the Ryugu Palace, even asking if Zoro and Sanji can sense it too. At Punk Hazard, he was able to sense the Yeti Cool Brothers attacking Chopper and Nami. He was able to sense that Rebecca had no true killing intention towards him even when she was attacking him. During the Corrida Colosseum Block C battle royale, he was able to successfully dodge all the weapons Jean Ango threw at him. He can also use the ability to measure the strength of an individual as seen when he complimented Duke Inuarashi's superior strength at a glance.
Luffy seems to have also mastered Busoshoku Haki to a extremely high extent, which has been shown to darken his body (or parts of it) and harden it. This is first shown being used when he easily defeated a Pacifista with a single Haki imbued punch used in conjunction with his Gear Second. He is also able to use his Gear Third in conjunction with his Busoshoku Haki, being capable of knocking out a giant beast such as the Kraken easily, despite the great disadvantage of being under water (where his power was considerably weaker).
Another demonstration of Luffy's Busoshoku Haki is during his fight with Hody Jones, where he was able to harden his arm, leg, and forehead for both strong offensive and defensive measures. The defense of his Busoshoku Haki, however, is not absolute; while it is good for reinforcing his near immunity against blunt attacks, it is currently not strong enough to defend against sharp objects, such as Hody Jones' shark teeth or Doflamingo's strings. However, this issue is more apparent when facing exceptionally sharp weapons or more powerful opponents, as a small amount of Luffy's Haki used on his forehead was strong enough to shatter Rebecca's sword on impact when she was forced by Doflamingo to attack Viola.
After the air bubble was produced and merged with Noah, Luffy used Busoshoku Haki combined with Gear Second to perform "Gomu Gomu no Red Hawk", which causes his fist to ignite into flames and create an explosion after it hits the target.
Luffy was later seen being able to knock back a Logia user like Caribou at considerable distance, something he was never able to do before the timeskip, without exploiting the Logia Fruit's weakness. He was also able to grab Smoker's arm in its smoke state as if it was solid, and was also able to grab and punch Caesar Clown in his partial Logia state.
- Busoshoku: Koka (武装色 硬化 Busō-shoku: Kōka?, literally meaning: "Color of Armaments: Hardening"): Luffy uses Busoshoku Haki to harden his body (or parts of it). It was used for the first time against the Kraken in conjunction with Gear Third to harden his enlarged arm to the point of it attaining a completely dark and shiny appearance, in order to use his "Gomu Gomu no Elephant Gun". In the FUNimation subs, it is called Armament; Hardening.
- Atama Buso (頭武装 Atama Busō?, literally meaning "Head Armament"): Luffy imbues his forehead with Busoshoku Haki to harden it. This is first used in preparation for a "Gomu Gomu no Kane" against the Iron Shell Squadron. In the FUNimation subs, it is called Head; Hardening.
- Gear Second Buso (ギア２（セカンド）武装 Gia Sekando Busō?, literally meaning "Gear Second Armament"): Luffy imbues his fist with Busoshoku Haki while under the effect of Gear Second to harden it, which also seems to have the added effect of igniting it. It was first used in preparation for "Gomu Gomu no Red Hawk" against Hody Jones.