Perseus Branwen

Percy is killed in the PJ universe. He is reincarnated into the RWBY universe as Qrow Branwen's son. His appearance is basically the same except that his right eye is the same red as his father's. He is taught by his father how to use different weapons and how to survive on his own. His semblance is his powers from his previous life except they're amped up to Poseidon from God of War 3 levels. When he calls upon his semblance, sea-green lightning sparks off of him like Deku using One for All. His semblance also boosts his strength, speed, agility, endurance, healing, stamina, and intelligence. His semblance also adds the abilities to control lightning, cause plagues, change gender, clone himself, and fly. He also inherited the Branwen bird magic. He can turn into a bluejay. He goes to Beacon during Ruby's first year to due to his semblance. He befriends RWBY and JNPR. He also befriends CVFY later on. He saves Pyrrha from Cinder. He gets into an one-on-one battle against Raven and comes out on top. He also heals Amber. You can pick the pairing or have it be a harem.

Monster Musume/PJ

Percy is killed and reincarnated into the world of Monster Musume. When he wakes up, he sees a female centaur with wings and a hellhound turned into a girl. He learns that they're Mrs O'Leary and Blackjack. Follow Percy as he gets a harem, creates hijinks, and gets laid.

Highschool DxD/PJ

The Olympians heard about God creating Sacred Gears, so they created the Olympian Gear. The Olympian Gear has the powers of all of the deities on the council, the minor gods, and the deities that were forced into doing it such as Susanoo. Poseidon created several gears and put them into his son. The Earth Shaker amplifies his earthquake powers up to off the Richter scale. The Sea God's Rage amplifies his water powers to creating hundreds of meters tall tsunamis. The Storm God's Wrath amplifies his storm powers allowing him to create blizzards, thunderstorms, and lightning storms. All of the gears combined form Poseidon's Rage. Percy has to move to Japan after the Giant War because of Paul's job. He goes to Kuoh Academy, meets the devils, dies, reincarnates into Rias's pawn, steals 4 of Issei's pawns, steals Issei's harem and expands his harem.