It's possible that I fell in love a while back.
Atsushi had caused Kouichi to develop a fear of dark spaces by locking him up in a warehouse seven years ago. Atsushi now lives in remorse about what he had done. One day, Kouichi confronts Atsushi and suggests, "If you're truly sorry, then let's be together."
Could it be that desire for someone else's heart drives one to force their love upon that person?