Ayuha Samaru is a high school student. She is honest and works hard at everything, no matter what. One day, she has trouble at a gyudon restaurant due to money. A man at the restaurant, Yoshitaka Hiromitsu, helps her out. The next day, she finds that Yoshitaka Hiromitsu has come to her school as a substitute teacher for her ill homeroom teacher. Ayuha Samaru now believes that Yoshitaka Hiromitsu is her fate in love. She keeps expressing her feelings to him.

A group of boys and girls, twelve in total, gather at an abandoned hospital to die for various different reasons. There, they find the body of a dead boy. The group of twelve attempt to find the person who killed the boy. During their search, the reasons why they want to die are revealed.

The series follow the story of a high school boy who lives in Tokyo, and his childhood friend, Hakatano Donko-chan, who is from Hakata and really talks in Hakata dialect! People around her sometimes get confused because of it, but her dialect makes them smile!