He claims to have killed his family and at least a thousand other people. His mother was a prostitute and, due to her profession, he knows nothing about his father. Even so, he made a silent oath to look after his mother until his father came home. When he was fifteen, Genjuro killed a man who stayed in their home -due to his mother's pleas for protection from her client's drunken rage. While he turned to leave his home for good, she attacked Genjuro while cursing his existence and left the scar on his back. He killed her in retaliation.

Orphaned, Nicotine Caffeine spotted him and took him under his tutelage along with Haohmaru in his home. Both students were close friends yet Genjuro's hunger for power worried Nicotine. To test his students, he tempted them to fight over the treasured sword, Fugudoku. They were tested by facing off with a group of other fighters. Genjuro, believing that "worthless" people don't deserve life, killed his opponents during the competition. He leaves Nicotine's place in disgust after this event. He swore to kill Haohmaru and Nicotine, spiteful for their idealistic beliefs on swordplay. He hates Haohmaru especially, because he resembles the man his mother was with when he killed them. He also was attracted to Shiki at one point, as she resembled his mother.

His profession during his travels is a hitokiri or killer-for-hire, often accepting the more "dirty" jobs such as wiping out pirate brigades and bandit hideouts. His former clients include Sankuro Yorozu and Mizuki Rashojin. In Samurai Shodown 64-2, Genjuro gains the upper hand in his last duel with Haohmaru. Before he could deal the final blow, a boy stabs him in vengeance for his unnamed father. It's heavily implied that Genjuro dies from his wound and, as promised, an older Haohmaru toasts to his friend's honor.

Similar to Ukyo, his death is believed to be retconned in the newer sequel. Here, Genjuro is attacked by two assassins; one he kills quickly and the other somehow survived. Before he makes the killing blow, the surviving assassin tells him that this was a test from a man named Golba and offers him to join his master. As he hesitates, the assassin blows himself up, which perks Genjuro's interest and begins his journey to find Golba. He is still alive in his ending and is on another job as usual.

He has a motto that he recites before he goes to slaughter people. It's roughly translated as:

"I build a nest of beast in my heart. The fang is growling; Kill... Let's go kill. The fang is crying; Kill... Let's go kill. To calm it down, I have no way but slash men..." (translation taken from here)

Although it is mostly exclusive to the series's drama CDs, players can hear parts of it being sung by a woman during his theme song in Samurai Shodown 64.

Genjuro is a brutal warrior who only fights for the pleasure of killing. He likes to dominate over others and hates people who are weak. There are times when he occasionally feels regretful and shows mercy for his actions though he often counteracts these instances with more acts of cruelty. He is often called a "demon" by his victims, usually moments before he slays them.

Samurai Spirits 2

(Source: Kyosei, SNK Wikia)