Beelzebub-jou no Okinimesu mama.

Summary:

Beelzebub is a great demon lord who rules over several millions of demons. Myurin, who decides to serve the demon lord, learns that not only does Beelzebub lack the poise of a great demon, but is also a laid-back girl who likes fluffy things. Thus begins the daily-life comedy revolving around the many villains in the demon world.

Summaries provided by MyAnimeList.net