So when this girl was young, she was bullied by her entire school especially by the main protagonist. Nobody cared for her and her parents abandoned her but she held no grudge against the people who mistreated her. When she grew up, nobody offered her a job because everyone in the village despised her for no reason. She ends up living in the outskirts of the town and tries to search for magic in a land where it got sealed so she could use it to help the people so they can see her differently. While she was searching she stumbles upon a demonic essence and it fuses itself with her altering the way she thinks but not possessing her. She ends up having a black heart and when she finds the magic she goes on a killing spree and kills the main characters child and wife with an unborn child. After her killing spree, she promotes herself to the goddess of magic and summons up a black hole to "purge" the world of its people. So what do you think?
Man tbh that sounds pretty cool but try to give her more of a reason for people to dislike her, and maybe as her being a goddess she could also be having like a confliction withe her self still to give her current situation more depth but it's sound cool keep on keepin on.