Seems that after meeting Necro for the first time, she treated nicely and he gave her much care and attention. He offered her a collar as a symbol of friendship and she gladly accepted it. Little did she realize just what it was, as soon as the cursed collar hit her neck, it sealed itself closed as the clasp disppeared. She could feel dark energies starting to swirl around as she quickly started to transform into a succubus. Necro took a liking to his work. After a while it wears off and she becomes her normal self again. Nenamoi now can activate this collar at any time and can now easly control her new form, or, Necro can just will it to happen as he sees fit. She acutally likes her new for and magic that comes with it, who knew becoming a sex demon would do the trick.

Art, and Necro are both  koekoek19
Nenamoi and story are mine :D