Tanabe is the probation officer overseeing Hajime Shiroishi after his release from Kantou Boys' Medical Center, where Hajime was confined for a violent crime. Tasked with guiding Hajime's rehabilitation and reintegration, Tanabe adopts the role of mentor. He recognizes Hajime's underlying potential for extreme violence and deliberately manipulates this trait. Tanabe strategically channels Hajime's unstable psyche and violent impulses to advance his own goals, effectively weaponizing the young man. This calculated manipulation directly triggers Hajime's transformation into the psychopathic killer known as Ichi, with Tanabe orchestrating the necessary conditions. Tanabe thus emerges as a key facilitator of Ichi's origin, leveraging his institutional authority to exploit vulnerability for personal ends.