Hisao Nakai is a normal high school student, currently in his final year of high school. One day Hisao finds an anonymous letter in his math textbook, directing him to meet the sender at a given location. The sender turns out to be his crush, however, as she confesses to him, he suddenly collapses. He awakes in a hospital bed, and is told by the doctors that the reason he collapsed is due to arrhythmia, a rare heart condition that causes his heartbeat to sometimes become irregular. Due to this, his parents have enrolled him in Yamaku, a school for (physically) disabled students.