Daisuke transforms into Dark (usually unwillingly) whenever he experiences feelings of love or intimacy. Daisuke is kind hearted, the opposite of Dark, and is always trying to stop Dark from performing crazy stunts to no avail. Later in the series, Daisuke gradually falls in love with Risa Harada's(his crush) older twin sister, Riku Harada. Riku in turn also has feelings for Daisuke.
He regularly argues with Dark but, expresses concern for him when he is in danger. He misses Dark when they are separated in the series through magic. In the anime adaptation, he cries when Dark seals himself and Krad, leaving Daisuke.
Poundmon,the Fists of Reliability
The Crest of Reliability
The Digi-Egg of Reliability