Perhaps a plot where the Oc is on a quest to discover more about his mother, Ophis. Along the way, he forms unlikely alliances with both friends and foes, and has to navigate through various dangerous situations. For example, he could be seeking ancient artifacts related to Ophis that are scattered across different realms. This would lead him to encounter different cultures and powers within the supernatural world.
One interesting plot idea could be the Son of Ophis struggling to fit into the world of Highschool DxD. He might have powers that are both a blessing and a curse. For example, his powers could attract unwanted attention from various factions in the supernatural world, leading to constant battles and challenges.
One idea could be that the OC, as the son of Ozai, struggles with the dark legacy his father left. He could try to redeem his family name by using his firebending skills for good, like helping to rebuild the Fire Nation in a more just way.
Perhaps the OC son of Doomsday is hunted by various groups who fear his potential. He has to constantly be on the run while also trying to discover his true origin and the purpose of his existence. He could meet a group of outcasts who help him hide and in return, he uses his powers to defend them.
One idea could be that the OC, as the son of Hades, struggles with the stigma associated with his father's realm. He could be trying to prove that he's not all about death and darkness. For example, he might use his powers to help the living in secret, like saving people from disasters that are on the verge of happening.
One plot idea could be the OC's struggle to live up to his father Hephaestus' reputation. He might face challenges in creating unique and powerful artifacts, while also dealing with the expectations of the other gods. Another could be a quest to retrieve a lost, powerful weapon made by Hephaestus that only his son can sense. The OC could also get involved in a love story where his skills as a son of Hephaestus play a role, like creating a special gift for his beloved.
One idea could be the OC's struggle to live up to his father's reputation. He might face challenges within the Lannister family, like dealing with his siblings' envy or rivalry. Another could be his role in the political games of Westeros, perhaps trying to form alliances different from his father's.
One idea could be the OC's struggle to prove himself worthy in the eyes of his father, Stannis. He might face challenges like being overshadowed by his father's more well - known followers. Another plot could involve the OC getting involved in the power struggles of Westeros, trying to uphold his father's claim to the Iron Throne while also forging his own path. Maybe he discovers a hidden secret about his family that changes everything.
One idea could be that the OC has to deal with the legacy of Black Widow. He might struggle with living up to her name while also trying to carve out his own identity in the superhero world.
One plot idea could be that Naruto is somehow transported to the world of Highschool DxD and meets Ophis. Maybe he has to help the characters in Highschool DxD deal with a threat using his ninja skills, and in the process, he forms an alliance with Ophis.
I'm not entirely sure as there are many different interpretations in fanfiction. But generally, it might involve Harry having some special powers or a different destiny due to being the son of Ophis. It could also explore new relationships with other characters from the Harry Potter universe and new adventures that deviate from the original story.