|Debut:||Chapter 704; Episode 632|
|Affiliations:||Happo Navy; Chinjao Family|
|Occupations:||Leader of the Happo Navy; Martial Artist (Viz: Fighter)|
|Japanese VA:||Kōichi Hashimoto|
Sai is a thick built man with shaggy brown hair and sideburns. He has an usually smooth and tubular torso, and in spite of his muscular strength he lacks defined abs, or a belly button.
He sports a dark cape with a white frill collar. He wears puffy blue and yellow thick-striped pants and dark shoes. He has the number "13" tattooed on his left side just below his ribs, similar to the tattoo of the number "12" his grandfather has, representing that he is the 13th leader of the Happo Navy.
When transformed into a toy, he appears as a monkey bearing cymbals. He has rounded teeth and a well-defined lower jaw. He wears a bow tie, sunglasses, a stripped hat, and a pair of pants that resemble those he wore as a human.
Sai believes in honesty and fairness, as he stood up for Luffy when he was about to be unfairly disqualified. He is very emotional and has a habit of overreacting whenever he rejects something, repeatedly insisting there is no need for it before turning belligerent toward the offering party. This also goes for apologizing, as he threw himself on his knees and begged for forgiveness from a Colosseum doctor after having already apologized three times. Sai is responsible, being quick to restrain his grandfather's rash attack on Luffy (in disguise as Lucy) and Cavendish so that it would not interfere with their true goal at the tournament.
Sai is thoroughly dedicated to his training in the Hasshoken, notably restraining his natural brotherly emotions towards Boo in remain focused in battle. However, as the commander of the Happo Army, he is also mindful of and fully dedicated to towards his comrades in arms, and will ruthlessly avenge their defeat.
Sai cares greatly for his grandfather as he got angry with the Colosseum's medical staff for not telling him what happened to Chinjao. He also acts as a guide for Chinjao since he prevented the elderly pirate from clashing with Luffy and Cavendish and ruining their “mission.” Chinjao shouted when his grandson was grabbed by Trébol, but, after Sai and Boo were turned into toys, Chinjao completely forgot about them due to the effect of the transformation on loved ones.
Sai is very attached to his brother, which we saw when Boo was defeated by the Funk Brothers. Because of his Hasshoken training, Sai isn’t supposed to have a deep attachment to Boo when in battle to prevent him from getting distracted but does have enough pride to avenge any of his fallen comrades, including his brother. Boo also acts as a guide for Sai similar to the relationship between Sai and Chinjao as Boo had to hold back his brother from attacking Luffy.
Sai has a strong dislike for Doflamingo for giving weapons to his country's enemies and instigating wars. He has vowed to stop this illegal trade and get revenge on the Shichibukai.
Trébol and SugarEdit
After Sai was imprisoned in an underground dungeon, Trébol abducted him and Sugar turned him into a toy. Trébol hypnotized Sai and took control of him. The Happo Navy leader was frustrated and confused at how he was physically forced to follow Trébol’s orders and wasn’t able to control his own body.
Monkey D. LuffyEdit
When Luffy was about to be disqualified for knocking out Spartan before the matches started, Sai defended him, saying that Spartan was the one who instigated the fight. Afterwards, Luffy thanked Sai for defending him only for Sai the get belligerent and angry. After he was restrained, Sai flicked off Luffy. Sai does not seem to hold a grudge against Luffy for winning Block C. He even tried to get Luffy's attention so his grandfather could thank him.
Though Sai doesn’t have any actual qualms with the Funk Brothers outside of the Corrida Colosseum match, he did defeat them in battle to specifically avenge his beaten brother.
Sai shares a mutual respect for Ideo as a fighter, as seen during their battle in C Block.
Riku Dold IIIEdit
Sai blames Riku Dold III for letting Doflamingo come to power.
Abilities and PowersEdit
Little is known about Sai's powers, but he is renowned as a martial artist able to use a technique which generates vibrations. He was able along with Boo to restrain back his enraged grandfather, although it is probable that Chinjao didn't exert himself fully as he wouldn't wish to harm his grandchildren.
What is certain is that Sai is strong enough to handle and excel against the dangers of the New World, to the extent of being chosen as the 12th Commander Happo Navy in succession of the legendary Chinjao. In the Block C battle royale of the Corrida Colosseum, he demonstrated enough might as a fighter to effortlessly dodge the assault of the combined Funk Brothers and defeat them in one blow, as well as spar evenly with Ideo , a boxer powerful enough to launch a giant out of the ring with a single punch. Although Luffy knocked Sai easily out of the arena with a Gear 2nd kick, the attack was a surprise that caught him off guard, and he was shown to be conscious and fine in the waters right after.
Sai was seen using a sword when attempting to lunge at Luffy. It is currently unknown how skilled he is at using this weapon.
In the fight at Block C, he used a bladed polearm proficiently. Sai acrobatically hurls himself at his enemy by balancing on his polearm and swinging himself in their direction, in a manner similar to pole vaulting. Sai can use the momentum generated by such an assault to land kicks and other attacks on his foes.
Sai, Boo, and Chinjao came from the Flower Country to compete for the Mera Mera no Mi and with a hidden agenda to investigate a weapons trade that the Donquixote Family is involved in. For the battle royale, he was placed in Block C.
After Lucy defeated Spartan before the competition had officially started, one of the colosseum staff was about to disqualify the disguised Straw Hat captain for causing a fight before the match. Before he could follow through with this threat, the Chinjao Family arrived on the scene. Having seen the entire thing first-hand, Sai demanded that the staff member quit trying to throw Lucy out of the competition, as it had been the "big guy" who had started the whole thing, and if anyone should be thrown out, it should be him. After Lucy thanked them for standing up for him, Sai laughed and said there was no need for thanks. He then started repeatedly declaring that Lucy's thanks weren't needed, before angrily demanding for him to take it back. Before he could attack the bewildered Lucy, he was held back by Boo, who apologized to the confused pirate, stating that he's the kind of man who gets easily fired up. Hearing this, Sai angrily repeated his comrade's words, before flipping Lucy off as he was dragged away.
Later, when Chinjao attempted to kill Lucy because of his vendetta with Garp, Sai and Boo held him back before his anger went out of control. They then explained to him that he could just kill Lucy during C block, reminding him of their true goal.
After this, Sai is seen along with the rest of the Chinjao Family as he enters the ring, prepared to begin Block C's battle royale.
Later, as the battle royale commenced, Sai, along with Chinjao, Boo, Jean Ango, and the Funk Brothers, was seen watching as Lucy plow through his fellow competitors while riding on the back of Fighting Bull.
Shortly thereafter, he dodged a fighter's attack by using his polearm as a pole vault, and then kicked the man's shield, utilizing the Hasshoken technique to easily disarm and defeat the fighter. Later, when Boo was being mercilessly pounded by the Funk Brothers, Sai called out to him in alarm  and later avenged his brother by knocking out the Funk Brothers with a single kick. After the Funk Brothers' defeat, he was then locked in combat with Ideo. The two fought evenly, exchanging blows with each other. However, before one of them could finish off the other, they were caught in the middle of Lucy and Chinjao's feud. Lucy knocked Sai out of the ring with a single kick while charging at Chinjao.
While floating on the water outside of the ring, Sai and Boo watched Chinjao's clash with Lucy. Upon witnessing Chinjao's defeat, they called out to him in horror as he fell and sank into the water.
After the match's conclusion, Sai and Boo brought Chinjao to Luffy so he could thank him for restoring his old head.
Sometime later in the underground medical treatment facility, Sai was seen in the waiting room. He was yelling at a doctor because he has not seen his grandfather leave the treatment room. Sai was then told that Chinjao went through another exit and he apologized profusely for his outburst. When it was Sai's turn to receive treatment, he laid on the examination table. It was then revealed to be a trapdoor and Sai fell down into an underground dungeon filled with broken toys. After seeing that some of the other disqualified participants were also thrown down there, Sai demanded to know what was going on and how would they be able to get out.
Sai could only sit and watch as more of the defeated contestants, including Boo, dropped into the dungeon. After Ricky is revealed to be the former king of Dressrosa, Riku Dold III, Sai revealed the Chinjao Family's objective and blamed the former king for allowing Doflamingo to rise to power which led to wars in various countries including the Flower Country. Sai was then abducted by Trébol and transformed into a toy. After his transformation, Sai found himself unable to disobey Trébol's commands.
Sai was later seen in the underground trade port, moving crates and still unable to disobey the orders given to him.
- Sai vs. Corrida Colosseum Group C gladiators