"Teacher," a sacred job of protecting and guiding students. In this world where magic users and non-magic users coexist, alone lives the sorcerer Solo. He is also known as the skilled assassin "No.0," who always carries out any request he receives. As part of a certain mission, he is assigned to teach at a magic school, but the class he's assigned to teach is Class D, a class consisting of dropouts. While desperately playing the role of a teacher in order to complete his mission, a transfer student arrives and things take an unexpected turn... A school fantasy unfolding between the strongest assassin as a fake teacher, and the evilest of students who serve as his "targets!"