Okay,crazy idea. What if,Percy was never a son of Poseidon. What if he was Luke's older twin brother?....

The Wizarding War has ended and Percy is ready to start at Hogwarts as Deputy Headmaster. But the aftermath of the war is not quite what he hoped it would be. The Wizarding World is wary of Percy and unsure of how to handle the Greek Pantheon. And there is still lingering trauma and resentment of those who chose the wrong side... While Percy navigates his new job, his relationship with Hermione, and his mysteriously failing health, he cannot help but be reminded of his first five years at Hogwarts. Because Percy's learning that to move forward in the future, he needs to come to terms with his past. Before it kills him. (Essentially, this is both a prequel and finale to the Nexus series)

Harry doesn't know who to trust. It's been a year since his cousin, Percy, disappeared-again. And at the end of Harry's sixth year, Dumbledore is dead. Harry feels lost and alone...until he, Ron, and Hermione receive the contents of the Last Will and Testament of Albus Dumbledore. With mysterious clues all pointing towards the Son of Poseidon, Harry knows he will see his cousin again soon. Sure enough, Percy shows up at the worst time, saves Harry's life, and joins the golden trio to hunt down the horcruxes and kill Voldemort.

A nexus is a connection between two groups. Percy is a demigod son of Poseidon, but he's also a wizard. Throughout his time at Camp Half Blood and Hogwarts, he has kept each half of his life secret from the other. But when a nasty break up with Annabeth requires Percy to turn to the Wizarding World for comfort, he discovers that a lot has happened during the year he was questing against Gaea. His best friend's oldest enemy has risen again. Rejoining his friends, the Golden Quartet, at Hogwarts turns out not to be the reprieve Percy was searching for. But he can't abandon them now when they need him most.

Born about two decades before the Trojan War, Perseus lost his mother because of Zeus' hatred of Poseidon and his children. He was rescued by a goddess who took him in along with his new brother, and they became a force to be reckoned with. (Sorry this summary sucks) Also, this is inspired by Timeless Warrior by Anaklusmos14, it isn't copied, but will be similar.