Over the course of his journey, Roronoa Zoro has been in situations where his techniques have had to adapt for one reason or another. In addition to his primary fighting style, he has several other related fighting styles that form the greater part of his Santoryu fighting abilities. Ittoryu (literally meaning "One Sword Style") is one of them.
These are the attacks he uses with one sword. As Zoro is left-handed, his Ittoryu techniques have nearly always been executed with his left hand. He usually uses Wado Ichimonji for them, but after the timeskip he seems to be proficient in using each of his three swords for his one-sword techniques. He mainly fights with one sword when not fighting seriously or when he is using a specialized cutting technique. Early in the series (when Sham stole two of his swords and Zoro had to fight him and Buchi with just one), Zoro himself claims that he is "not that good at one-sword techniques". However, over time, he seems to have worked on this weakness and becomes proficient with this style. In fact, most of his Ittoryu techniques are very powerful finishing techniques.
Ittoryu Iai: Shishi Sonson (一刀流 ｢居合｣ 獅子歌歌,Ittōryū Iai: Shishi Sonson?, literally meaning "One Sword Style Draw and Resheath Technique: Lion's Song"): Placing the sheathed sword upright and listening to the "breath" of his opponent, the attacker rapidly unsheathes, attacks, and resheathes their sword. An interesting note is that Zoro does the technique back-handed as opposed to from the waist with a standard grip on the sword. "Shishi Sonson" (子子孫孫) is a four-word proverb meaning one's offspring. This was first seen being used to finish off Mr. 1. Zoro uses this technique only when he needs to cut metal like Mr. 1's steel body or Kaku'sTekkai technique. This move was his very first Ittoryu attack. This attack is as powerful as Kaku's Rankyaku: Roudan. In the 4Kids dub this is called Single Sword Lion's Strike and in the FUNimation dub this is called One Sword Style: Lion's Strike, but in episode 299, this is changed to One Sword Style Sword Draw: Lion's Song. Also in the FUNimation dub, "breath" is referred to as "rhythm".
Sanjuroku Pound Ho (三十六煩悩（ポンド）鳳,Sanjūroku Pondo Hō?, kanji meaning "Phoenix of the 36 Earthly Desires"; furigana meaning "Pound Phoenix/Cannon"): This attack uses the air itself to slash the target from a distance. To initiate it, Zoro first holds one of his swords horizontally above the shoulder of his sword arm, and then performs a circular swing that launches the air compressed projectile spiraling towards the target. Zoro introduced this technique as a very powerful Flying Slash Attack. This was first seen being used to finish off Braham in Enel'sSurvival Game. The attack's name is actually a very heavy pun, it's written out as "Phoenix of the 36 Earthly Desires" in the manga with a skewed reading attached that makes it "36 Pound Ho" when read out. Ho means both Cannon and Phoenix, however the attached kanji is for Phoenix, making that the literal translation and the "Cannon" reading a Pun on that, both of which are correct. The "Pound" part is a skewed reading of the Kanji "Bonnou" for Earthly Desires, and it is referring to the Caliber of a Cannon. (a 36 Caliber Cannon would fire a 36 Pound Ball) This technique is known as 36 Pound Phoenix in the Viz Manga, 36 Caliber Phoenix in the FUNimation dub (and sometimes the Viz Manga) and Single Sword Rising Phoenix in the 4Kids dub.
Hiryu: Kaen (飛竜火焔,Hiryū: Kaen?, literally meaning "Flying Dragon: Blaze"): Using one sword wielded in his left hand with his right hand gripping his left wrist for support (or vice-versa), Zoro jumps high up into the air and slashes his opponent. After slashing them, Zoro's opponent then bursts into flames (in the anime, the color of the fire is blue instead) from where they were slashed. This was first seen being used against Ryuma. The animal or creature that usually accompanies Zoro in the background when performing powerful techniques is an occidental dragon. The dragon bares an uncanny resemblance to the dragon killed by Ryuma the King from Oda's earlier work, Monsters. The scene where Zoro slashes Ryuma with this technique also resembles the scene from Monsters, in which Ryuma slays the dragon. In the Viz Manga and FUNimation dub, this is called Flying Dragon Blaze, a translation of the original name.
This is a list showing the attacks Zoro used for his Ittoryu after his two years of training with Dracule Mihawk. The techniques he uses after the two years are mostly enhanced versions of his old ones.
Yakkodori (厄港鳥,Yakkōdori?, literally meaning "Disaster Harbor Bird"): Zoro launches from his sword a crescent moon-like projectile of compressed air to the opponent with great speed, similar to 36 Pound Cannon. "Yakko Odori" is a traditional Japanese dance. It was first seen used against Hody Jones. It was powerful enough to critically injure one of Hody's subordinates whom he used as a shield. In the Viz manga and FUNimation subs, this is called Bird Dance.
Sanbyakurokuju Pound Ho (三百六十煩悩鳳,Sanbyakurokuju-Ppondo Hō?, literally meaning "360 Pound Cannon"): Zoro delivers a stronger version of his 36 Pound Cannon, which is presumably 10 times stronger than the original. It was first seen used against a big fish the Straw Hat Pirates caught in their voyage to the New World. In the FUNimation subs, this is called 360-Pound Phoenix.
Ittoryu Iai: Shi Shishi Sonson (一刀流 “居合” “死・獅子歌歌”,Ittōryū Iai: Shi Shishi Sonson?, literally meaning "One Sword Style Draw and Resheath Technique: Lion's Song of Death"): A stronger version of his original "Ittoryu Iai: Shishi Sonson". Zoro swings his sword in a very quick and powerful unsheathe move to slice his opponent. This attack is strong enough to easily decapitate a legendary beast like a Dragon. It was first shown to decapitate the Punk Hazard dwelling dragon. In the Viz Manga, this is called Iai Death Lion Song but in the FUNimation subs it is called Lion Strike. In the english localization of the One Piece: Pirate Warriors 3, it is called Death Lion Song.
Daishinkan (大辰撼,Daishinkan?, literally meaning "Great Dragon Shock"): First used as a finisher move against Monet, Daishinkan consists of Zoro running towards his opponent with Shusui held outstretched in one arm. He then executes a two handed overhead swing used to split his opponent into two from the top down. The power of the move is such that even after cutting through Monet's snow body, the attack still resulted in a powerful shockwave that cut through the floor many meters ahead of him. In the FUNimation subs, this is called Great Dragon Shock.
Baki (馬鬼（バキ）,Baki?, literally meaning "Horse Demon"): After raising his sword above his head, Zoro delivers a powerful vertical slice to his opponent. This attack can easily slice through solid stone. It was first used to counter Pica's Bitestone.