Seiji, AKA "Mad Dog", is a boy with a demon right hand.  He is known as a delinquent and for getting into fights.  He also is looking for a girlfriend and girlfriends are hard to find with his reputation.  One morning he wakes up to find a girl in the place of his right hand.  And this is not just any girl though, she is Midori, a girl who has admired Seiji from afar for many years.  Now Seiji must figure out how to go to school and live a "normal" life with a little girl instead of a right hand.