Daisuke Niwa is the series protagonist who after turning 14 and confessing his love to and being rejected by his crush Risa Harada, discovers that an entity called Dark lives within him. Afterwards he transforms into Dark whenever he experiences feelings of love or intimacy with the girl he loves, but Dark can choose not to come out if he so wants. Initially this is Risa Harada, but after she rejects him, Daisuke finds himself falling in love with her twin sister, Riku Harada, who does return his feelings after realizing how kind-hearted and gentle he was. Perceptive, athletic, and artistic, Daisuke is also skilled in dodging traps, picking locks, and other thieving-type activities, due to the daily life-threatening trials his family has him undergo when he gets up in the morning and returns from school in the afternoons.
Source from Wikipeida