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.
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.
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.
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.
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.
A plot could be that Tsukune has a strange dream about Akasha one night. In the dream, she is in some kind of danger. When he wakes up, he can't shake off the feeling. So, he starts to search for any signs of trouble around Akasha. As he gets closer to her, he finds that there are some dark forces at work that are indeed targeting Akasha, and he has to use his own unique abilities (maybe some new ones he has developed) to protect her.
In a fanfiction plot, perhaps Tsukune gets into trouble with a group of bullies at school. Moka comes to his rescue and in the heat of the moment, they kiss. This kiss could be a moment of realization for both of them about their true feelings. After that, they start to secretly meet and have more romantic encounters. But they have to keep it a secret because of the rules at the school. Their relationship develops as they try to find a way to be together openly, with the kiss being the starting point of their journey.
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.
The plot could revolve around the baby's discovery of its powers. It might start with the baby accidentally using a new power, like being able to phase through walls or having super - strength. This would catch Moka and Tsukune off - guard, and they would then need to find out how to control these powers. Along the way, they could meet other characters from the Rosario Vampire series who either offer help or pose a threat to the family.
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.