Operating under the aliases "Jijii" or "Old Geezer," this central manipulator orchestrates conflict within the Anjo yakuza family. His true name is unknown; he asserts his aged appearance stems from plastic surgery, claiming actual age in the early thirties alongside an extremely muscular physique fueled by steroid abuse.

Jijii psychologically engineers Hajime Shiroishi (Ichi) into a lethal instrument through implanted false memories. These fabricated traumas include witnessing the rape of a classmate named Tachibana, fostering deep shame and conflating violence with sexual arousal. This conditioning enables Jijii to direct Ichi's assassinations of yakuza figures.

His primary scheme involves using Ichi to murder Anjo family head Yoshio Anjo and steal his fortune. Jijii enlists others like firearms specialist Noboru and heroin addict Inoue/Kano (with altered appearance) to further his goals. His manipulations extend to Karen, a hostess connected to yakuza enforcer Kakihara; Karen dies by Ichi's hand under Jijii's influence.

Jijii's machinations drive the fatal confrontation between Ichi and Kakihara, culminating in Kakihara's death and Ichi's psychological shift. After these events, Jijii is discovered hanged from a tree. The nature of his death—suicide or murder—remains ambiguous, though the proximity of Takeshi Kaneko (son of Kakihara's henchman Shuji Kaneko) hints at potential retaliation.

The animated prequel *Ichi the Killer: Episode 0* depicts Ichi's origin, including high school bullying and Jijii's psychological manipulation forging him into a killer, reinforcing Jijii's role in crafting Ichi's traumatic backstory and violent conditioning.