Daisuke Niwa is a 14 year-old-boy who has a special genetic ability: Whenever he sees or thinks about his crush, Risa Harada, he turns into the infamous phantom thief Dark. During the start of the anime, Daisuke carries a picture of Risa Harada in his back pocket for such occasion. This will continue until his love is returned.
Satoshi Hiwatari is a student at the same school as Daisuke and the Harada twins and also the Commander of the police force, heading the investigation on Dark. This is because he is a member of the Hikari family, a clan of artists which has opposed the Niwa family of thieves for centuries. Satoshi has Krad, Dark's opposite and, like him, part of the Hikari artwork "Black Wings", within him in much the same way Daisuke has Dark within him.