Former Angel with Wings. / The Assistant, a Complete Sadist.
Beelzebub and Mullin run across someone Beelzebub seems to know. His name is Astaroth, and he's surrounded by adoring girls. He calls himself Beelzebub's older brother, and starts going off on how much he loves Beelzebub. However, Astaroth starts to wonder about Mullin, and goes to visit the two while they were working, leaving behind is own work. But then Astaroth's assistant, Sargatanas, comes to get him, and he seems pretty afraid of her.
Aired 25/10/2018EP 3 - Former Angel with Wings. / The Assistant, a Complete Sadist.

2018
As Miss Beelzebub Likes it.
Murin's lands his dream job with the demon king he's always held in awe, but when his tenure begins, it turns out the demon king isn't quite what he expected...
(Source: Yen Press)