in past Akutagawa and Atsushi were together, and they were happy, until one day when Akutagawa broke up with Atsushi and left. Atsushi couldn't accept the fact he was alone again and he went crazy joining the bad side as a murderer

One day Akutagawa was sent on a mission with few other PM members, and when he was walking around subway he saw Atsushi after all those years, Atsushi saw him and out of reflex attacked with a gun he had not even thinking who's he's attacking