I wonder what kind of tagahanga Fiction to write...

Well, if you're a new tagahanga fiction author, I'd suggest picking the pinagmulan material you're most familiar with, and Pagsulat about it in canon style. It's simpler than alternate character interpretations, OCs, AUs, and anything else deviating (radically or otherwise) from the original source. It's also likely to garner less hate, even if it isn't incredibly original. Just don't rip off an existing episode.