Percy Jackson Ideas... enjoy
I am rarely fond of twin Main character stories, they rarely work and usually just supplant the main character but I have an idea that could sort of work... at least on paper. Basically an inverse of Percy in some ways. One who resents his mother for getting with Gabe when there was a better option. One who is more open about his or her hatred of the gods. One who resents Grover for being a poor protector. One who is tired of the crappy Greek world and rebels, who uses the general crap Percy has to deal with to go against the the Gods and their brother who allows himself to be a pawn.
A Werewolf Percy story, who is bitten and is abandoned by a great many others, and who turns against the fickle demigods and whatnot. Who becomes a terror to the world, tired of a long life of abuse and mistreatment and who loses that sense of loyalty that was burned out of him... ( I can see him hurting or killing Dionysius first... ) It would be fun to explore a darker, smarter percy...
Percy who gets therapy and starts to value himself, his life more than the crappy gods and fair weather friends called Demigods. The therapist would actually be Pandora who is trying to turn him against the gods for abusing her mortal children. She would teach Percy magic, use magic to get him to open up more and generally mold him into a powerful figure that stands up for himself and betters the world on his terms.