Three Sword Style

Santōryū (literally: three sword style) is a way of sword fighting that deals with the wielding of 3 daito katana; One in each hand and one in the mouth. There are many different techniques for this sword style, including "Tatsumaki", "Onigiri" and "Hyaku Hachi Pound Hou". Roronoa Zoro, the Swordsman and first mate of the Straw Hat Pirate Crew is the world famous Swordsman who uses that style.

History
Zoro first started developing "Nitōryū", or, two sword style, when he first started learning the ways of the sword. Defeated by his rival Kuina 2000 times, this only drove him to become stronger and stronger. One day, he challenged Kuina to the two thousand first match, confident as usual. Only this time, he wanted to fight with real swords. Zoro fought with his usual Nitouryuu, as Kuina fought with her Ittōryū (One sword style). At the end of the fight, Kuina once again came out on top. That would be the last time that the two rivals ever fought each other, because the next day Kuina lost her footing on some stairs, fell, and eventually died, or in an edited version for younger viewers lost against an opponent and was wounded to the point where she could never again fight. When Zoro was told this he was devastated, and he asked his sensei to give "Wadō Ichimonji" to him (Wadoō Ichimonji is Kuina's sword) so that he can carry on Kuina's and his dream to become the greatest swordsman. It was because of this, that Zoro started learning Santouryu, and which later drove him to become an extremely powerful swordsman, and Santouryu to be an extremely powerful style.

Santouryu Techniques

 * Oni Giri (Demon Slash/Devil's Cut) - The first technique Zoro learned in Santōryū, strong enough to cut large rocks in half.
 * Tora Gari (Tiger Hunting) - A technique from what is noticeable, it may utilize ki.
 * Tou Rou Nagashi (Bleeding the Wolf) - A technique used once against Hachan, he dodges his opponent's attacks while subsequently slashing his opponent in the abdomen.
 * 'Tatsumaki (Dragon Coil) - A technique, Zoro's first, that cuts the wind to create a tornado that not only creates a blender effect on the opponent, but sends them flying into the air. Is called Dragon Twister in the English anime.
 * Takanami (Hawk Wave) - Sends a cutting wave toward the opponent, only two swords are used in this technique. Doesn't seem to be a very powerful technique.
 * Yaki Oni Giri (Flaming Demon Cleave) - Same principle as "Oni Giri," except this time the user is on fire.
 * Ushi Bari (Bull Horns) - A technique where the user holds the swords in their hands in the air near their head to resemble bull horns, and then charging forward and attacking the opponent in several places on their body.
 * Gazami Dori (Crab Clutch) - A technique where the user holds their right sword near their head, and the sword in their left hand near their knee; all three swords pointing toward the right. The user attacks by quickly moving the right and left swords in their opposite directions, clamping the opponent like a crab claw.
 * ShiShi SonSon (Lion's Song) - Santouryu's most revolutionary technique, where the user focuses their "Breath" or "Ki" into one of there swords, and can cut through anything. Only one sword is used in this attack. Zoro used this technique on Mr.1, whom is made of steel due to his devil fruit power. It was used at the end of the fight, where it seemed like Zoro was going to die, he even said himself that he was at deaths border. He felt a calm, a breathing of sorts, which he focused with his thoughts through his sword and cut through Mr.1 like paper. Research into the phenomenon that happened to Zoro has concluded that it might have been "Ki" that Zoro felt and used, since in buddhist culture "Ki" is described as "Breath" and such. The techniques that Zoro uses after ShiShi SonSon seem to utilize "Ki"; more evidence to the assumption that he learned to use "Ki".
 * Sanjuu Roku Pondou Hou (36-Pound-Cannon| 36 Earthly Desires) - A devastating technique that sends a cutting wave of either "Ki" or wind toward the opponent. Only one sword is used in this attack.
 * Nanajuu Ni Pondou Hou (72-Pound Cannon| 72 Earthly Desires) - A devastating technique that sends two air cutting waves toward the opponent. Used once, so far, against Kaku.
 * Hyaku Hachi Pondou Hou (108-Pound-Cannon| 108 Earthly Desires) - A devastating technique that send three air cuttng waves toward the opponent. A lot stronger than SanjuuRoku or NanajuPondou Hou, devastating is probably an understatement for this attack.
 * Saikuru (Cycle| rhinoceros spin) - A technque that cuts everything around the user, or in Zoro's case, all the opponents around the user. Not cutting them per se (At least not fatally), but sending them flying away.
 * Karasumagari (Crow Demon Hunting) - A technique where the user jumps in the air and slings their arms inward cutting objects or opponents in front of them.
 * Nitōryuu Iai: Rashomon (Two swords style drawing swords: Rashomon) - A two sword technique where the user holds their swords in their scabbard, and when approaching the target/enemy they quickly unsheeth their swords and precisely cut the target/enemy vertically. This attack is so devastating that it split two train carts in half, but didn't harm any of the people inside of it. It seems to be similar to the Shishi Sonson using 2 swords instead of 1.
 * Gyuuki Yuzume (Cattle Demon Brave Hoof) - A technique where the user approaches their opponent and slashes them with two swords. It sort of resembles the samurai attacking tradition of which both warriors rush each other and cut one another, at the same time, when they meet (Though, in Zoro's case, his opponent used an attack on him first. Zoro dogded the attack and then slashed his opponent when he got near).
 * Ebima Yonezu Oni Giri (Charm Demon. Sleepless Nights. Demon Slash) - Same principle as "Oni Giri," but this time Zoro somehow makes his blades bend. The bending effect deals more damge to the opponent, and somehow widens the attack area.
 * Sanzen Sekai (Three Thousand Realms) - The only Ougi (Ultimate Secret) technique that has been shown in Santouryu, Zoro used it against Mihawk, though it is not completely known of what real damage this technique can do since it utterly failed against Mihawk. In the anime, during the Ocean's Dream arc, (filler) it was used against Luffy, but it was (apparently) blocked, so it's effects are still unknown. As it is an Ougi, so it's probably one of Zoro strongest techniques, but it was only used at the beginning of the series, and Zoro has deeply improved since then. Zoro puts two of his swords in an outward-bent L-shape, spins them in a circle and thrusts them at the opponent. It is supposedly a killing technique.