One day, Sonoko's mentor asked her to return to Akademi - but not to finish her education. He wanted her to investigate the possibility that a serial killer was present at Akademi, killing any girl who attempted to get close to a specific boy.

"Aishi-senpai, would you like to accompany me In finding this fiendous killer?" She asked her crush, Ryoba Aishi, her tone was cold and her face was Stoic and aloof.