Origin
The body of an adult but the brain of a child, Ichi killing desires are triggered by memories of the merciless bullies that ruined his childhood. Every murder he commits is a revenge against those that haunted him. Later on it is implied that all those memories might be just illusions planted in Ichi’s mind by his father-figure “Jii-san“, so that he could be such an effective weapon.
Ichi wears a superhero costume with a giant 1 stamped on his back (Ichi means 1 in Japanese) and kills people with an axe attached to his left heel. Since he’s turned on by the sight of violence, death and wounds, every time he kills people he develops an erection and he’s forced to masturbate to calm down. At the same times, once he’s finished, he cries out of desperation, feeling guilty for these actions.
Other Media
In the 2001 movie he’s played by actor Nao Omori.