GASP! That reminds me Mabel and Grunkle Ford from Gravity Falls. Maybe, she lost her mind because she found out her super powers, and killed Dipper, Stan and others. She liked to kill and now she's unstoppable. IT'S JUST MY THEORY GUYS
When I did this in 2017 there was no context, BUT NOW, Zero (the guy) is like a kind of "dad" to Marry (the girl) and realizes that sometimes Marry is acting very differently. She is possessed by Colin (the boy) who loves her and wants her just for him, and tries to kill Zero because of his jealousy. (sorry if something is misspelled 😔)
Demon:Wants that guy dead. The guy: R U N Muslim: AUZUBILLAHI MINASHAITHANIRAJIM!!!! (I SEEK REFUGE IN ALLAH FROM THE OUTCAST SHAITHAN(DEVIL/DEMON)!!!)