That song is an offering from the Reapers-a Requiem very near the boundary between heaven and hell where one’s soul returns to. There, all possessing the same aspiration of becoming a Reaper, cadets pair up with one another to study in order to become a fully fledged Reaper. In that place is a school in which Reapers-beings that collect human souls-are developed and trained. Assembled as “Reaper Cadets” at this school are the protagonist and her peers who were once human.

The protagonist, Cocoro, wasn’t selected by anybody to be her partner as she performed poorly in all disciplines of Reaper study. The other attendees of these supplementary lessons are fellow Reaper cadets. It’s filled with unique guys, all with their own reasons for attending the school. As a result, she was grouped with other cadets that were falling behind, and was made to take special supplementary lessons.