Definitely Naruto and Issei. Issei is all about his perverted ways and getting stronger, while Naruto is focused on protecting his friends and achieving his dreams. Their clash of personalities would be really interesting. Naruto might not understand Issei's obsession with girls at first and try to set him straight. And Issei would be amazed by Naruto's power and want to learn from him.
The interactions between Naruto and Akeno would be quite fascinating. Akeno has her own allure and power. Naruto, being godlike, would be an enigma to her. She might be intrigued by his powers and his different way of looking at things. They could have some deep conversations about power, morality, and the differences between their two worlds while also having some light - hearted moments due to Naruto's sometimes clueless nature about the more flirty aspects of Akeno's personality.
Itachi and Rias would be really interesting. Rias is used to being in control and having power, but Itachi's calm and collected nature along with his overwhelming power would put her in a different position. She would likely be intrigued by his Sharingan and his combat abilities. Itachi, on the other hand, would be dealing with a different kind of power structure and would have to navigate the social hierarchy of the devils in Highschool DxD.
The interaction between Illya and Rias would be really interesting. Rias is a powerful devil with a lot of charm and leadership. Illya, on the other hand, is a magical girl with her own set of powers. They could start off as rivals, both vying for the attention or respect of other characters, but then realize they have more in common and can work together.
Another interesting interaction could be between Naruto and Akeno. Akeno is known for her mischievous nature. When she meets Naruto, she would be curious about his ninja skills. Maybe she would try to play some pranks on him using her magic, but Naruto, with his quick reflexes and shadow clone jutsu, would be able to turn the tables on her. This would lead to a really fun and dynamic relationship between the two characters.
Naruto and Issei would be really interesting. Naruto, with his positive and determined attitude, would contrast with Issei's more pervy and hot - blooded nature. They could learn a lot from each other. Another interesting interaction could be Naruto and Sirzechs. Sirzechs, as a powerful devil king, would be intrigued by Naruto's power source, the Juubi. And Naruto would be interested in Sirzechs' leadership and power management in the devil world.
I think Naruto would be the most interesting. His energetic and determined personality would stand out in the Highschool DxD world. He could bring his ninja way of life and values, which are quite different from the devilish and angelic cultures in DxD. His ability to make friends easily might also lead to some really unique interactions with the DxD characters.
Naruto and Rias would be really interesting. Naruto's straightforward and determined personality combined with Rias' leadership and strategic mind could lead to some great interactions. They could learn from each other's fighting styles and ways of dealing with problems in their respective worlds.
Definitely Naruto himself. His positive attitude and never - give - up spirit would contrast greatly with the more morally ambiguous characters in Highschool DxD. He could also introduce the concept of chakra and ninja techniques, which would be completely new to the Highschool DxD world. His rasengan, for example, would be a very powerful and unique ability in that universe.
Naruto himself would be a great choice. His sunny personality and strong will would contrast with the more complex and often morally ambiguous characters in Highschool DxD. He could bring a sense of innocence and pure determination to the world of DxD, and his unique jutsu would be a new and exciting addition to the battles there.
Ichigo and Issei would be really interesting. Ichigo, with his calm and collected nature most of the time, compared to Issei's more pervy and hot - headed ways. Their different personalities could lead to some really funny and intense interactions, especially when it comes to fighting side by side or arguing about battle strategies.