Neighbor No 13 Story
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.
This is the best place to read Neighbor No 13 online.
And here are the reasons why.
Q: Is this the official site for Neighbor No 13?
A: No, The entire site is fan-made.