History:
As a child, Soujirou was the illegitimate son of a kindly rice merchant who died while Soujirou was still very young. Left in the "care" of his abusive relatives, he was beaten often for the slightest offenses and treated like a slave. Eventually he began to smile when faced with such abuses, having learned that his relatives would be put off by his seeming cheerfulness and stop their beatings sooner.
One day, the criminal Shishio Makoto came to town, freshly burned by government agents and fleeing the police. In a classic case of "wrong place, wrong time," Soujirou witnessed Shishio's massacre of a group of policemen, and was swiftly caught by Shishio. Soujirou's smile saved his life, intriguing Shishio and staying his hand.
With the promise of his life in return for bandages, food and water, Soujirou hid Shishio in the rice shed and stole provisions for him, often having conversations as Shishio tended to his wounds. It was then when Shishio first exposed Soujirou to his philosophy of "the strong rule, the weak die," and he gifted Soujirou with a wakazashi.
Soujirou's relatives eventually discovered Soujirou's thefts, and attempted to kill him. But armed with a new wakazashi and fearing for his life, Soujirou desperately but methodically slaughtered them all. It was in those moments that he completely surpressed what was left of his emotions, leaving only a happy, smiling boy who would go on to become Shishio's apprentice assassin.
It was years later when Soujirou, as Shishio's right-hand man, fought Himura Kenshin. The battle seriously shook Soujirou from the beginning, as he was unable to understand how Kenshin could be so strong if he refused to kill. The philosophy ingrained in him by Shishio - the strong live, the weak die - failed to reconcile with what he was experiencing as he fought Kenshin. As the shaky meaning he had given his existence fell apart, so too did the barriers in his mind that had kept his emotions at bay for years. Soujirou snapped, unable to fight at peak strength as his emotions left him easy to read, and Kenshin won the battle.
It was because of this fight and because of Kenshin's wise words that Soujirou returned the wakazashi that Shishio had given him as a child, and began his own wanderings in a quest to find new meaning for his life.
Personality:
Soujirou is extremely polite and well-mannered, and appears to be cheerful more often than not. These days, he's capable of other emotions as well, but prefers to fall back on his old habit of smiling all the time when unsure of a situation.
Skills:
Soujirou a master swordsman of Tenbu no Sai Niyoru Ken, a unique style developed and used solely by him. Soujirou is capable of moving at speeds so fast that, to an observer, it appears that the distance between Soujirou and his opponent has shrunk - hence it's given title of Shukuchi, which means "reduced earth". He's also well-versed in battoujutsu. Combining the Shukuchi with battoujutsu, Soujirou invented his ultimate move - Shuntensatsu, or Instant Divine Kill - named such because the attack is so swift that his opponent dies instantly before they can feel pain, almost as if they were struck down by a divine force. Soujirou's abilities have earned him the title "Tenken" or Divine Sword.
In Game:
Soujirou has a dog tail and his tattoo is located on the back of his neck.