Daisuke Niwa has just turned 14 years old. He secretly has a crush on Risa Harada which seems to cause him some troubles. Unknown to him his family have a secret condition which causes the young men of the family to turn into the infamous phantom thief Dark Mousy whenever they run into the girl they love.

Daisuke must learn to control his emotions for Risa without awaking the powers of Dark Mousy. As well his mother has decided to use Daisuke’s powers as Dark to fight off evil demons that have possessed famous pieces of artwork. Daisuke now has to deal with all of this while trying to keep his secret hidden from the police and Satoshi Hiwatari, the adopted son of a high ranking police officer.