One of the most popular crossover scenarios might be the ones that involve unique power combinations. For example, in a Naruto and Highschool DxD crossover, Naruto's jutsu combined with the devil powers in Highschool DxD could create really interesting battles. In a Rosario Vampire and Highschool DxD crossover, the different types of supernatural beings from both series could interact in new and exciting ways. Also, crossovers that explore the different school settings and how the characters from each series adapt to them are quite popular.
In these fanfictions, the power systems can interact in some really cool ways. Naruto's chakra system is very different from the devil powers in Highschool DxD. But when combined, you could have a situation where Naruto's chakra is used to enhance a devil's attack. In Rosario Vampire, the vampire powers are more about physical abilities and some magic. They could interact with Naruto's ninjutsu in a way that creates new forms of combat, like a vampire using Naruto's shadow clone jutsu to create multiple decoys.
I'm not sure if there is such a specific fanfiction where a character from Rosario Vampire is reading Naruto fanfiction. Fanfiction can be very diverse, but this seems like a rather unique and specific concept. It's possible that it might exist in the vast realm of fan - created stories, but it would be quite difficult to find without a more targeted search.
Well, for a fanfiction like this, Naruto could bring his ninja training and knowledge of different jutsus. Shinso's presence would add a psychological aspect as he can mess with people's minds. They could get involved in the power struggles in the Vampire Highschool DxD world. Maybe they side with a particular group, like the Gremory family, and help them in their battles against other factions. It would be a story full of action, mystery, and new friendships as Naruto and Shinso navigate this strange new world.
One possible fanfiction could involve Naruto's ninja skills in the world of Vampire Highschool DxD. Maybe he uses his shadow clone jutsu to outwit the devils and vampires. Shinso could use his mind - control quirk from My Hero Academia (assuming that's where he's from in this crossover) to manipulate the various supernatural beings. It would be a chaotic yet exciting mix of different anime universes.
One idea could be that Naruto is somehow transported to the world of Highschool DxD. He could use his ninja skills and chakra in the new world, maybe even teach some of the characters there a thing or two about combat. For example, he could show Issei how to better control his power using chakra control techniques.
The storylines can be combined by creating a common threat. Suppose an enemy emerges that is interested in both the power of the Bijuu and the power sources in Highschool DxD. This would force the characters from both universes to team up. Also, the cultural differences between the Naruto world and the Highschool DxD world can be explored. Naruto could introduce concepts like ninja clans and shinobi training to the DxD characters, while they could introduce him to the complex social hierarchies and supernatural politics in their world.
Love and relationships are also common. For example, a vampire character might fall in love with a non - vampire character, creating a Romeo - Juliet - like situation. There could be difficulties due to their different natures. Another aspect is the exploration of the vampire's origin. Many fanfictions will dig into how the vampire came to be in the 'Highschool DxD' world, whether it was through a curse, a scientific experiment gone wrong, or some other means. This origin story often ties into the overall plot and character development.
The female characters from Highschool DxD, like Rias, would be intrigued by the unique personalities of the Naruto characters. Rias might see potential in some of them to join her peerage. And the Naruto girls, like Sakura, would be a bit shocked at first by the more revealing outfits and flirty nature of some of the Highschool DxD characters. But over time, they would bond over things like protecting their friends and the school. The Naruto boys would respect the power of the Highschool DxD devils and might even try to incorporate some of their fighting strategies into their own ninja combat styles.
One idea could be a crossover where Naruto characters end up in the Rosario + Vampire world. For example, Naruto could be mistaken for a powerful yokai due to his chakra. Sakura might study the unique magic in the Rosario + Vampire world. Another could be a vampire in the Naruto world, using their powers in a different way than the normal jutsu.