As he approaches his 14th birthday, Daisuke Niwa, a clumsy and unremarkable middle school student, decides to confess his love to Risa Harada, only to face rejection. But a startling revelation awaits him: whenever he thinks of Risa, he transforms into Dark Mousy, a notorious phantom thief. Unaware of his family's secret past, Daisuke's mother has groomed him to continue their legacy of art thievery. Caught in a web of uncertainty and familial expectations, Daisuke navigates strained relationships with peers and kin. Soon, he discovers that his destined rival may be the last person he wants to confront.