**Miki** is the landlord at the place the Devil King stays, "Villa Rosa Sasazuka". She requested that her apartment be rented out to "shady characters" such as Maou and Alciel. She seems to have some knowledge of Ente Isla.

Spoiler

She is a guardian of the Earth and is thought to be incredibly powerful to the point where Sariel and Gabriel did not strike Villa Rosa Sasazuka out of fear of provoking her. She is older than any known archangels in history.

(Source: Hataraku Maou-sama Wikia)