It could be a story of self - discovery. The Emiya clan character has lost their memory and ends up in the Rosario Vampire world. Haru takes it upon herself to help this stranger. As they journey together, the Emiya clan character starts to regain bits of their memory through various encounters. Haru, in the process, also discovers new things about herself. They both grow as characters and their bond becomes unbreakable as they face different challenges in the Rosario Vampire world.
Perhaps in the fanfiction, there is a competition of sorts. The Emiya clan member challenges the other characters in Rosario Vampire, including Haru, to a series of tests of strength and intelligence. Haru, seeing this as an opportunity to learn and grow, accepts. As they compete, they start to respect each other more and more, and eventually form a strong friendship. This friendship then leads to them protecting the Rosario Vampire world together from external threats.
One possible fanfiction could be about a member of the Emiya clan finding themselves in the world of Rosario Vampire. They might encounter Haru and form an unexpected alliance. Maybe they team up to face a common threat in the Rosario Vampire universe, using the unique skills of the Emiya clan and Haru's own abilities.
One idea could be Shirou finding himself in the Rosario Vampire world and having to adapt to its unique rules. Maybe he uses his skills from his own world to protect the school from various threats that are different from what he's used to.
One possible plot could be a new student from the Emiya clan arriving at the Youkai Academy. This student has a unique power that no one has seen before. The other students are both curious and a bit intimidated. As the story progresses, the new student has to face challenges in classes that are specifically designed for youkai skills, like shape - shifting combat or magic spellcasting. Along the way, they make friends with some unlikely youkai and together they uncover a mystery about the academy's past that threatens its present.
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.
The plot could be about Mizore facing challenges due to her pregnancy in a world filled with vampires and other supernatural beings. For instance, she might have to deal with the prejudices of some of the more traditional vampires who don't think a pregnant ice monster should be part of their society. This could create a lot of drama and conflict as she tries to prove herself and find her place.
The plot could involve a magical forehead flick. Maybe there's a spell that can only be activated by a flick on the forehead. A character discovers this spell and uses it to help their friends in a dangerous situation. For instance, they flick the forehead of a vampire who has been cursed and it breaks the curse. This could lead to an adventure where they have to find out more about the origin of the spell and protect it from those who would use it for evil in the Rosario Vampire universe.
In a Naruko x Rosario Vampire crossover fanfiction, the plot could center around a tournament. The idea could be that both the ninja world and the Rosario Vampire world participate in a grand tournament to prove which world has the stronger fighters. Naruko would be one of the representatives from her world. She would face off against the various characters from Rosario Vampire. This would lead to some interesting battles and also some unexpected friendships as they learn about each other's cultures and fighting styles.
Well, one possibility could be that Naruto is somehow transported to the Rosario Vampire world. He might see the vampires as a threat to the innocent humans there and decide to banish them. Maybe he uses his shadow clone jutsu to create a diversion while he sets up a powerful sealing jutsu to send the vampires to another dimension.
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.
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.