Isekai Reincarnation is a thing, apparently

An OC/SI HP fic that I might continue. Standard deal, reincarnate into Harry Potter as a side character that didn't exist. Unfortunately for the world, this one is extremely knowledgeable on fantasy and mythical magic systems. Even with that though, they more want to subtly change things for the better. (OP but more manipulator OC. Slytherin OC. Gender up to interpretation)