The story begins with Sanda, a second-year middle school student, being attacked with a kitchen knife by his classmate Fuyumura. Although Sanda initially couldn't make sense of the situation, he gradually came to believe that Fuyumura's actions were merely mean acts stemming from the latter's peculiar puberty phase. However, that was all actually a misunderstanding. Fuyumura is seriously questioning whether Sanda is actually the descendant of a certain family...