A big typhoon that happens once every few years.Let's go home early today... I thought so, but before I knew it, it was the usual time.Trains were suspended... Roads were flooded... In the end I ended up staying at school.That was the time. "Teacher... What are you doing until this hour?" Utsumi, a student, was also left behind at school.Alone in a large school building until morning, a dangerous and obscene night was about to begin.