I will suggest some ideas that came to mind for this amazing story that you maybe could use
1. the demon is actually in love with the reader and wants her for himself which adrian wont allow, or the demon does it purely because he wants his children to be extremely powerful
2. a new character interferes and has a crush on adrian and tries to steal him away
3. reader gets pregnant which complicates things on finding the demon
4. marinette becomes good friends with reader and mar ends up dying to the demon
5. reader loses control and ends up killing innocents or the demon which makes everyone but chat noir afraid of her and everyone hunts her down but he decides to protect and hide her
6. reader loses her powers after that demon took it and she is left venerable but adrian protects her still
7. adding another character but they turn up to be the mastermind behind all the chaos
8. recruiting more people with similar powers to take down the demon (you can decide what else to add to that)
9. things turn dirty and twisted so that either reader loses a bet or she is bound to do whatever adrian says even if she doesnt like it (she thinks XD)
10. reader has bad memories of the past and only really cared about her mother because her father either use to beat her mom or try to do unspeakable things to her (he could also still be alive and working with the demon)
I hope you liked my ideas , you can even combine the ones you like the most and add your own ideas, and yes i know some of them are kind of weird XD
