Hisao Nakai is a normal high school student, currently in his final year of high school. One day Hisao receives a letter from parties unknown in his locker and waits at the written place for the sender. The person who wrote the letter turns out to be his crush; while speaking to her, 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 disabled students of all kinds.