Percy Jackson and the Olympians/Highschool DxD.
Plot: Percy Jackson left America due to being betrayed by Annabeth and the Gods as well as the demi-gods. While crossing the world he has an encounter that changes him from a normal demi-god into a half god half devil.
Rules: Percy was betrayed by Annabeth who cheated on him with another demi-god.
The gods betray him out of fear for how powerful he is.
The demi-gods betray him because they don't want to face the wrath of the gods.
While travelling the world he makes allies with different factions such as the devils, the Norse Gods, The Shinto Gods, and the Yoaki faction.
He must become a devil by either joining a peerage or one of his ancestors was a devil and while on the verge of death he activated his devil blood in order to live.
Percy should be one of the strongest in the world but don't make him to Op.
Forbidden: Percy can't have a sacred gear he must use his own power.
Percy can not forgive Annabeth and get back together with her.
Percy can't forgive the gods if a fight every breaks out and the Gods are losing he won't help them.
This should be a harem fanfic. Percy/Rias/Akeno/Sona/whoever else you want to add.