Sister-sama no Oose no Mama ni

One day, the demon Claude appears in front of the novice nun Sister Chris Ibarakawa. He says that he made a contract with Chris's estranged father, whose final wish was for Chris to live a happy life. Claude, who is very serious even for a demon, tells her "I will do anything to make you happy," by using all of his demonic powers.... Will Chris be able to stay on the pure and righteous path?

(Source: Comic Fuz, translated)