someone told me that after the last scene kesa slept on wataru's bed and the lights were off then morito arrived and had made his mind to keep the promise so he goes inside wataru and kesa's room then he killed wataru but when he got out of the house the head he saw he was holding is kesa's .. at that time wataru was still not home....I'm not sure if this is exactly what happened since in the story it was left open..