I was planning on creating some characters as DM for our next adventure because we ran out of our current ones. I asked the players about their preferred character, race, profession, backstory, etc to make the game more fun to play when one player who was playing super long said that she did not want to create an "regular" character because she is bored of using the characters over and over again. She planned on using a Succubus who was neutral because she wanted an more "interesting" gaming challenge. I agreed, then ran out of ideas on character traits.
The Succubus, on the MM, is a demon who charms people to do evil acts, so the only possible explanation is that the Succubus is a traitor to its own kind and decides to follow the "right" path, using it's skills for the "right" thing. Almost all of the players flaws and personality traits are about her past, and how she harmed innocent people, because that is the only ones I can think of.
That leads to a new problem: since she doesn't want to harm people and that is the incentive for her to betray her race, all she would do is to charm and to judge, sort of like a paladin: How do I play a paladin without being a stick in the mud? , but none of the methods work here. The only way I can think of for a monster to be in the party is that it wants to do good, but then they have to be a "stick in the mud", and is not fun for the other players. I am looking for additional set of character traits that does not give such an awkward situation.