transmigration harem bl

so this a bl where a guy gets transmigrated into a novel his sister likes (i think) the novel it’s about a girl who has like 5 guys that like her or something like that. so the guy gets transmigrated into a family and him and his cousin were the villains of the original story. now that he is in the story everything changes and his cousin (a girl) start going out with the ogfl and the guys all are after him if i remember correctly there is magic in this world and i think he can’t use it so he uses stones ig and he has brown hair i think his name was mathias (idk)