Three years after her resignation from Kurogin Academy, Yankumi returns as the new homeroom teacher of Akadou Academy's 3-D! Upon her arrival, she discovers that the class is full of delinquents, and is divided into two opposing groups that are always at each other's throats. One of the students, Kazama Ren, is suspected to be behind a series of muggings, and while the rest of the class doesn't seem to care about his predicament, Yankumi resolves to prove Kazama's innocence.