Jinchin was originally Ieyasu Sabanada, the eldest son of a samurai family that became counselors to the Imperial Court. However, after the death of his father, Ieyasu entered into a feud with his eldest brother for the control of the Sabanada Clan. Defeated and stripped of everything, he entered the distant Temple of Kagaii as a monk, taking the name Jinchin.
In the years at the monastery, his ambition grew and soon Jinchin started gathering an army, first of loyal monks at the monastery, then later ronin and rebellious samurai and at last attracting also oni, tengu, and legions of undead gakken.
In 1356 DR, he attacked the Kanazaki Province, first clashing with Doin Sanehiro at the Battle of Kiroshima, where to defeat the samurai Jinchin had to send his most powerful oni to kill him. Later, he discovered that Doin had survived and decided that he must die, because Doin had started a revolt to free the land conquered by Jinchin but also because the Earth Spider needeed the spirit woman Onoye, one of Doin's companions, to free himself.
Initially, Ieyasu only wanted control of his clan, but as Jinchin he wanted to rule over all Kozakura. He likeed showing his talents but tried to suppress all emotions, despite becoming obsessed by Doin's continued survival. He was a supreme strategist and a master fighter and shukenja. He killed only if he had to, but in his mind, murder and mercy were equal if they served his ends.