The main character, Soichi Senjo, is a high school student attending Yanogiyama Gakuen.

One day, Soichi meets a girl with a strange atmosphere when she is having lunch on the rooftop of the school. She has a disease caused by a mysterious virus called "black line disease" and was a transfer student who moved to receive treatment for the it.

Soichi will live with Suzune at the request of Ryoko Kunimi, who is also the doctor in charge of Suzune and his guardian.