Cheeky Angel

Megumi-chan is a girl with a secret past. She used to be a boy until she met a person she thought was a magic user. This person gave him/her a magical book from which a genie appears to grant one wish when blood is applied to it. Megumi made the wish to be a man in a man's body but the genie has a twist: he grants wishes backwards so he turns Megumi-kun aged 9 to Megumi-chan. (myanimelist.net)