Mei

Mei (메이) is a witch with a single snake demon.

Biography
Mei is saved by a snake and turns him into her demon, naming him Chen. She has killed countless witches but planned to return Chen to the afterlife until Noir interfered, convincing Chen to betray her.

After the betrayal, Mei is kept in captivity and locked away in the basement of the demons' headquarters until it was finally time for Chen to switch bodies with Mei. After they switch bodies, their death is implied but not explicit.