He was originally a samurai for a lord until a tragic incident occurred when he was escorting the son of his lord. On a mountain path, the boy slipped and fell to his death despite Sanshobo's best efforts to save him. At this loss, there was only one way to repay his lord for his failure, and his own son noted that he understood what was involved. At that, that boy deliberately leapt to his own death.
At that incident, Sanshobo resigned his post to become a monk and has helped Miyamoto Usagi in his adventures numerous times. That help was most significant in the "Grasscutter" and "Grasscutter II" where he played an important role in helping the rabbit ronin deal with the recovery of the legendary sword, Kusanagi and how to dispose of it.
Another significant development in those stories is when he sheltered the female fugitive, Inazuma when he found her unconscious. However, when Sanshobo and some subordinates return from investigating a strange occurrence that involved Usagi and the villain, Jei, they find their brethren massacred and Inazuma missing. Sanshobo vows to find the murderer of his order, although he does not suspect Inazuma since she did not seem to be in any condition to commit such violence.
Sanshobo visits the original temple where the black soul first arose in Jei. There, he successfully exorcises as a similar entity possessing a peasant while learning about Jei's activities there. Now knowing that a malevolent spirit is likely involved in the attack on his temple, Sanshobo continues the hunt, and reunites with Usagi, Stray-Dog and Gen along and learns that Inazuma is possession by the black soul Jei and that she killed his brethren under his control. At that revelation, the monk insists on joining the hunters to find her and deal with the entity.
Eventually, the party finds Inazuma mortally wounded, and while the warriors hold off a horde of competing bounty hunters, Sanshobo attempts to exorcise Jei from Inazuma. After much difficulty, he is successful in driving out the spirit, allowing Inazuma to die in peace in the arms of one his companions who turned out to Inazuma's brother. However, the evil entity escaped to possess another monk, Hama, who then killed Sanshobo's sensitive comrade, Senzo, to cover his escape. Whether Sanshobo intends to hunt down this latest vessel for Jei is unrevealed for now.