Beelzebub-jou no Oki ni Mesu Mama.

Beelzebub--the formidable right hand of Satan--commands fear and respect throughout Pandemonium. What her underlings don't realize, though, is that she's an airhead with a love for all that is fluffy and adorable! The only thing she might enjoy more is teasing her new attendant, Mullin, who is learning that serving Beelzebub is both heaven and hell...

(Source: Yen Press)