Neighbor No. 13 (2005)

Akai goes to school to get back his son. In one of the classrooms, Juzo slides a bag across the floor, Akai suddenly reacts and shoots the bag. Juzo gets the shotgun from Akai and points it at him. Akai asks where his son is and Juzo says that he's inside the bag. Akai cries over his dead son and apologizes for the things he did. Juzo starts yelling and then parts ways with his other personality (symbolized by Juzo leaving the room seen at the beginning of the film where his other personality walked in). The last scene is a younger Juzo and Akai walking past apartment 13 (in construction) and Juzo's other personality is inside...

Alex