Japan has a rigid social culture and based on that is the first premise of this story. A murder. Kind of an stigma in that society. Is alright to kill a "devil" in these modern "civilized" times? Can you set many persons free with that action? "Be all you can be" "Try to be free" "Now you have no fears to live your life" "Mom never lies" Those are some of the phrases that 3 of the main characters heard that night of the incident but somehow; mostly by the social weight, they could not use that to construct a better life for themselves but finishing those 15 years since that murder revolving around a pain that do not let them grow. In a limbo without a mourning. There are other back stories with the same relationship Parents/sons. Very simple addressed but direct and effective.

Society makes norms and sometimes you can feel guilty about your acts but in the end the feelings are there.