Neighbor no 13 manga

Neighbor No 13 summary:

In grade school Juuzou was tortured by his classmates and develops an alter ego. Years later, Juuzou has to work with one of his bullies named Akai, who move into the apartment above his. As time progress Juuzou's revenge minded alter ego takes over and becomes a psychopathic killer. Made into Live action movie in 2005.