Daisuke Niwa is a clumsy, block-headed, and wimpy middle school student who has few redeeming qualities. On his 14th birthday, he finally decides to confess his love to his longtime crush Risa Harada, but is rejected. In an unexpected turn of events, however, Daisuke finds himself transforming into Dark Mousy, the infamous phantom thief, whenever his mind is set on Risa. Though Daisuke is unaware of this strange heritage, his mother is certainly not: since before the boy was born, his mother had been planning for him to steal valuable works of art and let the name of the elusive art thief be known. With doubt and confusion constantly clouding his mind, Daisuke finds himself struggling in his relationships with classmates and family. And it is not long before Daisuke realizes that he is not the only one with a fated family legacy—his greatest adversary could be the one classmate he is most unwilling to fight. Niwa Daisuke is your average teenager, until his fourteenth birthday. He tries to declare his love to the girl of his dreams, but fails. Suddenly, whenever he thinks about this girl he turns into the legendary phantom thief known as Dark. Daisuke's mother, very much aware of this, makes him turn into Dark and steal valuable works of art for a purpose unknown to Daisuke. As the story unfolds, he learns why, and about his classmate who seems to have the same ability.