A middle school student with little to offer, Daisuke Niwa suffers unrequited love for Risa Harada, his longtime crush. Seeking to finally confess his feelings on his 14th birthday, he is rejected, leaving him feeling even more dejected. But then, something strange occurs - whenever Daisuke thinks about Risa, he becomes Dark Mousy, a notorious thief. Though Daisuke is oblivious to his unusual powers, his mother has always known about them, and has been grooming him to become a master thief. As Daisuke attempts to navigate his complex relationships with his classmates and family, he realizes that his life is intricately linked to that of his greatest adversary - a classmate he never expected to face in battle. With doubt and confusion consuming him, Daisuke must embrace his strange destiny and become the hero he was born to be.