The Neighbor No. Thirteen

隣人13号

In elementary school, Juuzou was tortured by his classmates. Years later, he finds himself working with one of his former bullies, a man named Akai, who has moved into the apartment above his. As time progresses, Juuzou's revengeful alter-ego takes over and he becomes a psychopathic killer. (Source: MU) Included one-shots: Volume 2: Wakatake, Drive