One plot idea could be that Alucard and Edward are forced to fight due to a misunderstanding. Maybe a powerful, mysterious force is manipulating events behind the scenes, making each think the other is a threat to their world. Another could be a battle for a powerful, ancient artifact that both believe they should possess for different reasons.
Well, perhaps it could start with a magical rift that opens up between their two worlds, causing chaos in both. Alucard and Edward, being powerful in their own rights, initially see each other as the cause of the trouble. As they fight, they gradually realize they have a common enemy that is using their fight to further its own dark plans. So, they have to decide whether to continue fighting or team up.
The plot could be that Alucard is on a mission to take over a certain territory and Edward stands in his way as the protector of that place. So they engage in a series of battles.
A really interesting plot could be that a powerful spell binds Alucard and Anderson's powers together. They can't use their full abilities separately but when they work in harmony, they are unstoppable. This forces them to work together and they end up forming an unlikely friendship as they face various foes.
One plot idea could be Alucard and Seras going on a mission together in a modern city filled with new types of supernatural threats. They have to use their combined powers to take down an ancient evil that has been awakened. Another could be a story where Seras struggles with her human emotions while Alucard tries to teach her how to better control her vampiric nature. It could also be interesting to see a story where they are transported to an alternate universe and have to find their way back while facing different versions of themselves.
In a 'alucard vs edward fanfic', the author might take creative liberties with the characters' abilities. Alucard, being a powerful vampire - like character, could have abilities like super strength, shape - shifting, and immortality. Edward, depending on which 'Edward' is being referred to, might have his own set of unique skills, perhaps magic or some form of combat expertise. The fanfic could be an exciting exploration of how these abilities interact in a battle or a tense encounter.
One plot idea could be that Jacob and Edward have to team up to protect their shared territory from a new threat. They start off distrusting each other but as they face challenges, they learn to respect and rely on one another.
One idea could be that Harry and Edward find themselves in a magical realm together where they have to solve a series of puzzles to save their world. They could use their unique skills, Harry's magic from his wizarding world and Edward's vampire abilities.
One plot idea could be that Alucard and Anderson are forced to team up against a common enemy, like a new breed of vampires that are immune to their usual methods of destruction. They start off hating each other but gradually gain respect as they fight side by side.
One idea could be that Pip, with his unwavering courage, helps Alucard face an ancient evil that even Alucard is hesitant about. Maybe they discover a new form of magic together during their adventure.
One idea could be that Alucard finds himself in a different realm or time period in the crossover. He could team up with characters from the other universe to fight a common evil that threatens both their worlds. For example, facing a powerful demon that has the ability to corrupt both the Castlevania world and the world he's crossed into.
Another plot could be about how their relationship changes during the pregnancy. Seras might become more vulnerable and rely on Alucard more, while Alucard has to learn to be more gentle and caring. For example, he might start to show a side of himself that he has kept hidden for a long time.