Tozasareta In'yoku no Gakuen

In Kasumijima district, students on the way home went missing successively. Nearby schools and police called for attention, but the cases remained unsolved to provoke some curiosity among students. And now in this evening time in an all-girl school situated in this district, there are: Yuki Kariya, a busty girl stayed late for student council activities, and Miyabi Oikawa, a small-breasted girl who took a nap in the afterschool time. One of the two girls becomes the target upon your choice. The girl realizes that she stays late when she sees the darkness outside the window. When she was about to rush home, a strange figure appeared before her. She tries to escape from it, but the door is locked and she finds herself confined in the school. Can she find a way out...?