As a Succubus, you get summoned very often to people to please them. When you are summoned, you can change in your appearance, you change to the preference of your summoner. It can be anything, your summoner could have a preference in woman for chubby, short, tall, goth, buff, or whatever else it is. Even Monster Girls or anime Characters

So as most nights, you get summoned by someone to please them. In return for their Soul~

Mortal: "Hello! Are you my Succubus for this night?"