Well, one possibility could be that Tsukune, being a vampire in the Rosario Vampire universe, somehow gets involved with the Sub Zero world. Maybe he has to face off against Sub Zero's enemies using his vampire powers. For example, he could use his super strength and speed to combat the ice-based attacks of Sub Zero's foes.
Tsukune could fit in as an outsider with unique abilities. His vampire powers would be a contrast to the ice - based powers in the Sub Zero world. He might be initially seen as a threat or a curiosity.
There are likely some good ones out there. It depends on what aspects of 'Vampire Rosario Tsukune is Zero' you are interested in. If you like character - driven stories, you might find fanfictions that really dig deep into the personalities of Tsukune and the other characters, perhaps showing their growth in different situations compared to the original story.
The plot could involve a quest. Maybe there is a powerful artifact that has been lost, and both Mizore and Sub Zero are somehow connected to it. Mizore might need the artifact to gain more power in the vampire world, and Sub Zero could be on a mission to keep it out of the wrong hands. Their paths cross, and at first, they are at odds. But as they learn more about the artifact and the forces that are after it, they join forces. For example, they might have to fight off demons who also want the artifact.
One possible scenario in this fanfiction could be that Vampire Rosario Mizore and Sub Zero find themselves in a strange, new realm. Maybe they initially see each other as threats due to their very different natures. Mizore, being a vampire, has her own set of powers like enhanced speed and the ability to charm, while Sub Zero has his ice - based powers. However, as the story progresses, they might realize they can help each other in some way, perhaps to defeat a common enemy that threatens both of their worlds.
First, know the characters well. Tsukune is a complex character with his own growth arc. Make sure to stay true to his personality. Also, understand the world of Rosario Vampire, like the different monster species and their cultures. Then, come up with an interesting plot. It could be a new adventure for Tsukune or a different take on his relationships.
You can expect a variety of things. Maybe some fanfictions will expand on the romantic relationships in the story. For example, there could be more in - depth exploration of the relationship between Tsukune and other characters. Or it could take a darker turn, exploring more of the dangerous and shadowy aspects of the vampire world that were only hinted at in the original.
In a fanfiction, Mizore might be accidentally transported to the Mortal Kombat realm where she meets Sub - Zero. At first, Sub - Zero is suspicious of her as she is an unknown entity. However, Mizore's shy and somewhat naive nature starts to soften Sub - Zero's tough exterior. They could then go on a journey to find a way to send Mizore back home, while also having adventures and fighting off various threats along the way.
They could have an epic battle. Sub - Zero's combat skills from Mortal Kombat and Mizore's speed and stealth from Rosario Vampire would make for an exciting fight. Maybe it starts because of a misunderstanding, like Sub - Zero thinking Mizore is a threat to his clan.
One possibility could be that Tsukune's death is a sacrifice to save his friends. In the Rosario Vampire world, he has made many friends and perhaps in the fanfiction, a powerful enemy threatens them all. Tsukune, being the selfless character he is, might give his life to ensure their safety. For example, if a dark and ancient vampire or a powerful monster attacks the school, Tsukune could use his unique powers (a combination of human and vampire abilities) in a final, all - out attack that costs him his life.
Tsukune's vampire form in fanfiction can vary greatly. Some authors might focus on the emotional aspect of him dealing with this new side of himself. He could struggle with the urge to feed on blood, or he might embrace it as a part of his new identity. Additionally, his relationships with other characters, especially Moka, can be significantly affected by his vampire form.