Well, in a fanfiction like this, Naruto characters could be integrated in multiple ways. First, their combat skills. Take Kakashi, for example. His Sharingan and vast array of jutsu would make him a formidable force in the Highschool DxD battles against devils and other supernatural beings. In Moka's world, he could use his skills to protect the school from any vampire - related threats. Also, Naruto's ideology of never giving up could influence the characters in both worlds, motivating them to keep fighting even in the toughest situations.
In the context of this fanfiction, Naruto characters can fit into the Highschool DxD and Moka's world through cultural exchange as well. Naruto's world has a strong sense of honor and loyalty among ninja clans. This could be introduced to the characters in Highschool DxD and Moka's world. For combat, characters like Rock Lee with his extreme taijutsu could participate in the battles in both worlds. His determination and hard - working spirit would be an inspiration. And Naruto's ability to connect with people on a deep level could help him form alliances with the different factions in both the Highschool DxD and Moka's world.
Naruto characters could fit in by bringing their unique abilities. For instance, Naruto's rasengan could be a new and powerful attack in the Highschool DxD world. And in Moka's world, his ability to make friends and inspire loyalty could be a big plus. His ninja skills would also be useful for dealing with the various threats in both worlds.
One possible fanfiction could be about Naruto somehow ending up in the world of Highschool DxD and meeting Moka. Maybe Naruto's skills and his never - give - up attitude would impress Moka and the other characters. He could teach them some of his ninja techniques, like the Shadow Clone Jutsu, which could be useful in battles against the devils and other supernatural beings in the Highschool DxD world.
A really interesting fanfiction could be where Naruto's Nine - Tails chakra has an unexpected reaction when he is near Moka. Maybe it flares up in a way that he can't control at first, and Moka's vampire instincts sense the power. This could lead to a situation where they have to work together to figure out how to control this new interaction between their powers. Also, Naruto could introduce the concept of ninja teams to the characters in Highschool DxD, which could change the way they approach battles and group activities.
Naruto characters can fit in by sharing their combat skills. For instance, Sasuke's Sharingan would be a powerful asset in the battles of Highschool DxD. It could give him an edge in detecting hidden enemies or predicting their moves. Also, Naruto's positive attitude towards his opponents could influence the way the more combative characters in Highschool DxD view their enemies.
Naruto characters can fit in by being exchange students. For instance, Naruto, Sasuke, and Sakura could be sent to the Highschool DxD world to study their magic and combat techniques. They would bring their ninja skills and unique personalities. Naruto's never - give - up attitude would stand out among the devils and angels, and he might inspire some of the characters there to be more persistent in their goals.
One interesting crossover could be the combination of Naruto's ninja skills with the supernatural elements of Highschool DxD. For example, Naruto's shadow clone jutsu could be used in the battles against the devils and fallen angels in the Highschool DxD world. And Moka from Rosario + Vampire (I assume that's what you mean by Moka) could use her vampire powers in new and creative ways when interacting with Naruto's characters. Maybe she could use her strength to compete with Naruto's taijutsu experts.
Some Naruto characters might also form unique relationships with Highschool DxD characters. For example, Sakura could become friends with some of the female characters in Highschool DxD and share her medical knowledge. Or Sasuke could be a rival to some of the strong male characters in the Highschool DxD universe, leading to intense battles and character development.
Shirou would fit in as a powerful and unique addition. His combat skills and magecraft would make him a formidable ally or opponent. He could use his projection abilities to create various weapons and tools, which would be very useful in the battles that often occur in the Highschool DxD world.
Well, he could be a transfer student. Just like any new character in the Highschool DxD world, Naruto could enter the school and immediately draw attention due to his strange powers and different appearance. His Juubi - influenced abilities would make him a target or an ally depending on who discovers him first.
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.
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.