Between heaven and hell, near the boundary where souls are sorted, there is a training school for Reapers—entities who collect human souls. The students enrolled there, called Reaper Cadets, were once human themselves. Cocoro, the protagonist, has failed every subject at the school and was not selected as anyone's partner in the mandatory pairing system. She has been placed in remedial classes with other students who are falling behind. The group in those supplementary lessons is unusual in its own ways. Cocoro needs to choose a partner from among these struggling Reaper cadets—and somewhere inside that choice, the story of a love that was not supposed to happen in this particular afterlife corridor begins.