They could interact in a training - centered story. Naruto characters could teach Highschool DxD characters about chakra and physical conditioning. Gabriel could then introduce her own form of spiritual training. In return, Highschool DxD characters could show the others about their unique magical items and powers. This exchange of knowledge and skills would create interesting dynamics among the characters from these three different universes.
Interaction could also happen in a school setting. If the Naruto characters somehow end up in the Highschool DxD school, they could join classes, participate in school activities, and make friends or enemies with the local students. There could be a lot of humorous situations as Naruto's more straightforward and energetic nature clashes with the more complex social dynamics of the Highschool DxD school.
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.
Well, characters like Naruto, with his friendly and determined nature, would likely befriend some of the Highschool DxD characters quickly. He might be curious about the different species in their world. And characters like Rias from Highschool DxD would probably be intrigued by Naruto's strong will and his ability to never give up, which is somewhat similar to the way devils in their world pursue power.
Kakashi would be very observant. He'd be quickly analyzing the powers and social structures in The Highschool of DxD. He might take on a mentoring role for some of the younger characters in both worlds. If there were any conflicts, he'd use his wisdom and combat skills to try and resolve them. And he could also learn from the more experienced characters in The Highschool of DxD, like Sirzechs. This exchange of knowledge and skills between the two groups of characters could create a rich and engaging fanfiction story.
The characters from Assassin could teach the Naruto characters some new stealth techniques. For instance, Ezio's parkour skills could be very useful for Naruto ninjas to move around more quickly and quietly. In Highschool DxD, the assassins could also help the devils in their battles by using their assassination skills to take out enemies without being noticed. And Naruto characters like Naruto himself could teach the others about the importance of friendship and never giving up, which could inspire the Highschool DxD characters.
One possible fanfiction could be about a crossover where the characters from Highschool DxD and Naruto are transported to a world where they meet Gabriel. Maybe they team up to fight a common enemy. For example, the devils from Highschool DxD and the ninjas from Naruto could combine their powers under Gabriel's guidance to defeat an ancient evil that threatens all three of their realms.
Naruto would probably be very friendly and curious. He'd be excited to meet all the different types of beings in the Highschool DxD world. He might start by trying to make friends with Issei, sharing his stories about his own battles and adventures in his world.
Naruto would probably be very curious about Gabriel. He's used to dealing with all kinds of strange and powerful beings in his own world, but Gabriel with her angelic nature would be something new. He might start by asking a lot of questions about her powers and the world she comes from.
One way to combine them could be in a crossover universe. For example, Naruto could be summoned to the world of Highschool DxD through some sort of magical mishap. Gabriel, being an angel in her own right, could be involved in a plot to either help Naruto return home or to use his power for some greater purpose in the Highschool DxD world. Maybe Naruto's unique abilities, like his shadow clones or rasengan, could be seen as strange and powerful in the DxD world, and Gabriel might have insights on how to control or enhance them.
Given Naruto's status as a yokai, his interactions with the Highschool DxD characters would be complex. He could be a source of mystery to them. With the perverted Issei, Naruto might find his behavior a bit off - putting at first but would gradually understand his character. When it comes to the more powerful characters like Sirzechs, Naruto would show respect but also not be intimidated. He could also form a sort of rivalry with some of the more combat - oriented characters, like Kiba, as they compete to see who is stronger in different types of battles, whether it's a one - on - one fight or a group battle against a common enemy.