|Occupation||Secretary on Detective Agency|
|Affiliation||Hell, Demon, Akutabe, Detective Agency|
|Sacrifice||Say "I Love You"|
|Anime Debut||Season 1, Episode 3|
Undine is a demoness serving a contract with Akutabe, acting as a form of secretary.
In her chibi form, Undine has pale green skin, medium-length blonde hair, round eyes, and a green fish tail. She wears a swimsuit top and is more humanoid compared to the more animalistic chibi forms of the other demons in the series.
In her hell form, Undine appears to be quite beautiful. She retains the form of a mermaid with pale green skin and longer blonde hair. Her eyes are usually shadowed by her fringe, which covers her right eye.
Undine represents Jealousy, which, in turn, appears to affect her personality in the human world. She is easily jealous of others and curses them with her abilities, typically making other women ugly enough to be unrecognizable. Undine has a one-sided crush on Akutabe, who uses her feelings to his gain on jobs. Undine is jealous of those who capture Akutabe's attention and is determined to make Akutabe love her through almost any means.
In Hell, however, Undine is shown to be very caring towards her ailing mother and is a dutiful daughter.