The Languid Diva is the fifth episode of the Seven Mortal Sins anime.
Lucifer next confronts and challenges Astaroth, the Demon Lord of Melancholy, who is making a living as an internet rock singer. Compelled by Maria's suggestion, Lucifer establishes herself as a singing idol in order to out-achieve Astaroth, which develops into a hard popularity contest once Astaroth receives Belial's and Belphegor's backing.
Finally, Astaroth ascends into the professional music world, but as her popularity grows, so does her insecurity. At the final showdown during her first live performance, Astaroth ends up sharing the stage with Lucifer and losing, but although she remains loyal to Belial, the parting of the adversaries ends up quite amicably. And as a reward for her efforts and dedication, Lucifer grants Maria the boon of addressing her more informally.
("Numbers indicate order of appearance")