Even if fanfic isn't the same you'd better bet I'll be writing a better ending. Also, I have various Soul Eater rps going on right now and I am DEFINITELY having my oc fight - and probably kill - Medusa in all of them.
My oc, Shiko, is the daughter of the devil, so she acts as sort of a "grim reaper" herself. She 100% has the power to throw Medusa into the darkest pits of hell and you bet she will. She is VERY protective of Crona, as they're the only thing keeping her chaotic soul from dragging her down into insanity, and would go absolutely ballistic once she heard about all the abuse Crona went through.
Basically my oc is just like me and would murder Medusa when given the chance.