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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.

Interestingly enough, Risa falls in love with Dark, and proceeds to do all sort of absurd things to get him to go out with her, which he eventually does. She has also kissed him on more than one occasion, and it is hinted that Dark loves Risa; but Dark claims that he does not love her, and that (according to the anime) Risa's grandmother, Rika, is the only woman he has ever loved.

Later in the series Daisuke falls in love with Riku, Risa's older twin although he doesn't realize it at first. Riku is hinted to have always had feelings for Daisuke but at first thinks that he only likes her because she is Risa's twin. Daisuke soon realizes his true feelings for her, as does she and their bond of love is formed.