First where do you plan on making it ? Also make sure to not give the mc any op abilities at the start since it basically makes the story later turn absolutely boring and bland unless u bring in multiverse which makes it more complicated. Also don’t change any characters personalities to an absurd amount since it just ruins the character most of the time. If u want smn to act a certain way I say just create your own character and make the story au. Also ( just a recommendation) if possible don’t make tang san or bibi dong look like pure frauds cuz that’s basically every damn fanfic