Weser

Background
He is The Pied Piper of Hamelin as revealed by Izayoi

Appearance
Weser has short, spiky black hair and wears piercings in his ears. His attire consists of a gray military shirt with the collar unfastened, gray pants and black combat boots. The style of his clothing is similar to that of a German army officer, based on his personifaction of the river Weser in the town of Hamelin.

Personality
A lot like Izayoi; cocky and won't give up. But he shows compassion to Izayoi as he fades away wishing him luck.

Relationships
Ratten - he works together with her, a low-level "Demon Lord" as well. They were both shown in the OP.

Gift
So far Weser has shown powers similar to those of a river, locking Izayoi in mud during their initial confrontation.