Midori Days(2004)

Midori no Hibi

High school delinquent Seiji Sawamura is desperate to have a girlfriend, especially after being rejected by 20 girls as of late. He's afraid that he will end his life with his right hand as his only companion. Apparently, that doesn't change when one day when he wakes up and discovers that his right hand has become a girl named Midori Kasugano, who confesses that she has had a crush on him for the last three years.

(Source: Anime News Network)