Taichi Yaegashi, Iori Nagase, Himeko Inaba, Yui Kiriyama, and Yoshifumi Aoki make up the Student Cultural Society at Yamaboshi High School, and one morning they discover that pairs of them have swapped bodies overnight. The entity responsible, Heartseed, offers no explanation and no end date, only amusement at the chaos. Each new phenomenon he inflicts strips away another layer of the group's defenses, forcing confessions and fractures they cannot take back.