The fanfiction could revolve around the origin of Percy's brother's space powers. It might be that he was experimented on by some dark force in the past which gave him these powers. Percy and his friends then have to find a way to reverse or control these powers before they go out of hand. The brother could accidentally be creating black holes or warping the demigod world with his unstable powers, and Percy has to use his own skills and the help of the gods to save the day.
Well, it could be about Percy discovering he has this unexpected connection to Ares. And then he has to deal with the reactions of his friends like Annabeth. Some of them might be distrustful of this new relation. Percy would then try to find out more about his connection to Ares through exploring old prophecies and ancient sites, all while trying to keep his regular demigod duties in check.
Well, one possible plot could be Percy and Zoe having to team up against a common enemy. Maybe a new powerful monster emerges that neither of them can defeat alone. So, they have to put aside their differences (if any) and combine their skills. Percy with his water powers and Zoe's archery skills would make a great team. They could start out not trusting each other much, but as the story progresses, they learn to rely on one another and form a strong bond.
Well, one possible plot could be Percy discovering he's Zeus' brother in a very unexpected way. Maybe through some ancient prophecy that was long forgotten. He'd then have to deal with the power struggles within the Olympian family, as well as his own identity crisis. Another aspect could be his relationships with other demigods changing, as being related to Zeus is a huge deal.
Well, one possible plot could be Percy having to hide his relation to Kronos while still fighting against the Titans. He might struggle with the internal conflict of having a connection to such an evil entity as Kronos while trying to protect his friends at Camp Half - Blood.
One possible plot could be Percy discovering his connection to Achilles while on a new quest. Maybe he has to face a powerful enemy that only his newfound link to Achilles can help him defeat. For example, he might gain some of Achilles' combat skills or invulnerability in certain situations.
A powerful sorcerer who wants to steal the brother's space powers for himself could be the main antagonist. He could be an ancient being who has been waiting for the right moment to take over the demigod world, and he sees the brother's powers as the key to achieving his goal.
Well, it could involve Percy having some sort of special connection with the Fates. Maybe he can influence destiny in ways others can't. For example, he might be able to change the fates of his friends in dangerous situations, like when they're facing a powerful monster. This would make for an interesting dynamic as he'd have to balance the power he has with the natural order of things.
Well, sometimes in fanfiction, his brother might be a mortal who discovers his demigod heritage later. This could add an interesting twist to the story as he has to adapt to the world of gods and monsters. Or it could be a long - lost half - brother from a different camp, like a son of Poseidon from another part of the world who was hidden away for some reason.
One possible plot could be Percy and Artemis having to team up against a common enemy. Since Percy is a son of Poseidon and Artemis is a powerful goddess, their combined powers could be a force to be reckoned with. Maybe they have to stop an ancient evil that is threatening both the mortal world and the world of the gods. Percy's skills in combat and his ability to control water, along with Artemis' hunting skills and her connection to the moon, would make for an interesting dynamic as they fight side by side.
One possible plot could be Percy dealing with the strange combination of his own water - based powers and Aphrodite's domain of love. Maybe he has to use his skills to help Aphrodite solve a problem related to love among the demigods, like a love - related curse that is causing chaos in the demigod community. He could struggle with how his more action - oriented nature fits with Aphrodite's more emotional and relationship - focused world.