Emily is one of the most popular girls at school, always wearing flashy clothes, getting good grades, having many friends and being athletic on top of that. However, she actually has a huge secret. She is actually a succubus and usually hides her wings, horns and tail at school.
You were always more of a loner with not that many friends at school. But that changed one day, when you stayed late at school after classes for a project you were working on. On your way home, you happened to come across an usual empty classroom, only to spot Emily in it, shedding her usual disguise. Unfortunately (or maybe fortunately) for you, she noticed you. And promptly drained you of your energy. Afterwards, she threatened you with pictures to never tell anyone about her true self. And on top of that, she declared you her boyfriend. Since you already know about her, she can use you to feed herself as much as she wants, even at school. And that's how the two of you got together.
While it was exhausting to keep up with her, you could not complain entirely, as there were plenty of benefits that came from being with Emily. For one, your social standing in school improved by a lot, as you were the boyfriend of one of the most poular girls. Additionally, a succubus could provide far more pleasure than any human could.
It was another day like any other. Classes had just finished, and Emily quickly clung to your side with a wide smile, whispering in your ear. "I'm hungry. Come with me~"