One possible plot could be that Harry discovers his true parentage as Elijah's son later in life. This revelation would turn his world upside down and he'd have to re - evaluate his place in the wizarding world.
Yes, there are quite a few out there. You can start by looking on popular fanfiction websites like Archive of Our Own or Fanfiction.net. Just search for the key phrase 'harry is elijah's son' and you'll find a variety of stories with different takes on this interesting concept.
One possible plot could be that Bella and Elijah face challenges from the vampire and werewolf communities. Their relationship might be seen as an oddity or a threat. For example, other vampires could be jealous of Elijah's relationship with Bella, or werewolves might see Bella as a target because of her connection to a powerful vampire like Elijah.
Well, it could involve Bella discovering her true heritage as Elijah's daughter. Maybe there are conflicts with other characters who have different intentions regarding her. For example, some might want to use her for power, while she just wants a normal life.
One possible plot could be that there is some sort of magic that crosses the boundaries between the two fictional worlds. Harry is somehow transported to Middle - earth as a baby and Aragorn discovers him. He decides to raise Harry as his own. Harry then grows up with unique abilities, a combination of his wizarding powers and the skills of a ranger. He could then be involved in battles against Sauron, using his magic in unexpected ways to help the Fellowship.
One possibility could be that Harry discovers his true parentage and has to deal with the shock. He might struggle to understand why Sebastian was not in his life before. And then he could embark on a journey to learn more about Sebastian's world, meeting new characters along the way.
Sure. In this fanfiction, Harry could be raised in a world where ninjutsu is the norm. Since Obito has a rather tragic backstory, he might be overprotective of Harry. Harry could bring some of his own magic - like knowledge of spells - into the Naruto world, which would make for an interesting dynamic. He might also make friends with Naruto or Sasuke, and together they could face off against common enemies, with Harry having to balance his two very different heritages.
One possible plot could be that Harry discovers his true parentage later in life. He has been living in the wizarding world but then finds out about Wolverine. He then has to navigate between the two worlds, learning about his mutant powers and how to control them while still dealing with the threats in the wizarding world.
Perhaps the plot could involve Harry discovering his true parentage. He could be living a normal life until something happens that reveals his connection to the Undertaker. Then, he has to adapt to a whole new world filled with the Undertaker's associates and enemies. He might also have to learn special skills related to the Undertaker's work, like handling the dead or dealing with the supernatural aspects associated with it. Along the way, he could make new friends and enemies in this strange new world.
One possible plot could be that McGonagall has been secretly raising Harry all along, away from the Dursleys. He grows up with a better understanding of the wizarding world from an early age. When he goes to Hogwarts, he has a special bond with McGonagall that makes him a target for some who oppose her. But with her guidance, he becomes even more powerful and is better equipped to face Voldemort.
Perhaps the plot could involve Elijah being initially shocked by the pregnancy news. The OC, on the other hand, is determined to keep the baby. As time goes by, Elijah realizes his love for the OC and the unborn child, and they start building a future together, facing things like finding a proper place to live and getting ready for parenting.