One idea could be a crossover with a popular fantasy series like 'The Lord of the Rings'. Imagine the characters from Trinity Blood in the Middle - earth setting, with vampires and other supernatural beings interacting with hobbits, elves, and humans. Another idea is a crossover with a superhero universe. The vampires in Trinity Blood having to face off against superheroes or even teaming up to fight a greater evil. For example, they could join forces with the Avengers.
A cool Trinity Blood crossover fanfiction could involve a time - travel aspect where characters from Trinity Blood end up in a different historical era, like the Victorian age. They would have to adapt to the new society while also dealing with their own powers and the politics of that time. Or, a crossover with a post - apocalyptic world. The vampires and other beings from Trinity Blood would have to survive in a world full of radiation and new, more dangerous mutants.
One idea could be that Naruto characters are transported to the Trinity Blood universe. Naruto, with his strong will and powerful chakra, might be seen as a threat or a potential ally in the complex political and religious landscape of Trinity Blood. For example, his shadow clone jutsu could be mistaken for some form of dark magic in that world.
Perhaps a crossover where the Trinity Seven characters enter a post - apocalyptic world. Their magic would be both a great asset and a source of danger as other survivors might see them as threats or saviors. They'd have to figure out how to survive and maybe even find a way to restore the world using their powers.
There are fanfictions that focus on alternate endings. Maybe in one, Abel Nightroad doesn't sacrifice himself and instead finds a way to bring peace without such a great cost. This type of fanfiction allows fans to explore different possibilities within the Trinity Blood universe.
One idea could be a crossover with 'The Vampire Diaries'. Picture Damon Salvatore showing up in Bon Temps and getting into a power struggle with some of the True Blood vampires. It would be full of drama and vampire politics.
One idea could be to cross it with a vampire - hunter themed story. The Black Blood Brothers could find themselves in a world where vampire hunters are more powerful and they have to team up with some unlikely allies to survive. Maybe a human detective who is initially after them but realizes they are not as bad as other vampires.
Maybe a character from True Blood, like Sookie, could travel to Forks. Her faerie abilities would be quite a novelty in the Twilight setting. The Cullens might be intrigued by her powers and her connection to the supernatural in a different way than they are used to. This could lead to all sorts of interactions, from alliances to rivalries.
A plot could revolve around a time - travel fanfiction. Maybe a character goes back in time and has to prevent an event that would have a catastrophic effect on the future of the Trinity Seven world. This could involve interacting with younger versions of the characters and changing their fates.
Another interesting concept is an OC who is from a completely different dimension but gets drawn into the Trinity Seven world. This OC could have a different set of values and magic rules from their own dimension, which would create a lot of interesting interactions and conflicts with the existing characters.
Abel Nightroad would be a great character to feature. His complex personality, being a vampire but also having a strong sense of justice, would make for interesting interactions in a crossover. Also, Esther Blanchett. She is a strong - willed human who could hold her own in different crossover scenarios. For example, in a crossover with a magical world, she could learn new spells and use her intelligence to navigate the new situation.
Perhaps a love triangle could be created in the crossover fanfiction. A female character from 'Twilight' could fall in love with a vampire from 'True Blood' while also having feelings for a character from her own world. This would create a complex web of relationships and loyalties, and the different vampire abilities and cultures from both series would add depth to the story.