There could be a fanfiction where Sasuke's Sharingan has an unexpected interaction with the supernatural elements in High School DxD. For example, his ability to see through illusions could be enhanced or altered by the magic in that world. This could lead to him having a different role in the battles and relationships within the High School DxD setting.
Well, Naruto's ability to use chakra and his various jutsu like the Rasengan could be adapted in the High School DxD world in some interesting ways. Maybe his chakra could be seen as a unique form of magic. Sasuke's Sharingan and his ninja skills could also be tweaked. For example, the Sharingan could give him an edge in detecting the movements of devils and angels in that universe. He could use his ninja stealth to his advantage in battles or when sneaking around in the DxD high school setting.
In a Naruto and High School DxD fanfiction, there could be a scenario where the protagonists of both stories meet in a neutral dimension. Issei from High School DxD might be intrigued by Naruto's ninja skills and determination. Naruto, in turn, could be curious about Issei's Sacred Gear. They could start training together, sharing their knowledge and skills, and ultimately have to face a common enemy that threatens both their worlds.
In a High School DxD fanfiction, Naruto and Sasuke's relationship could be a mix of old grudges and new alliances. They could start off on the wrong foot, with Sasuke being distrustful of Naruto's overly friendly nature towards everyone in the new high school environment. However, as time goes on, they would realize that they need each other. Naruto could help Sasuke open up more, and Sasuke could provide Naruto with a more strategic view of things. They might also team up against common enemies in the DxD world, like some of the more malicious devils or fallen angels. Their relationship would be a slow - burning one, with lots of ups and downs as they navigate the new world and their own personal growth.
I think Sasuke and Issei could make for a great combination. Issei is all about power and his perverted nature adds a comical element. Sasuke, on the other hand, is serious and highly skilled. Their dynamic could be really fun to explore. Issei might be in awe of Sasuke's skills and try to learn from him, while Sasuke could be both amused and irritated by Issei's antics.
One possible fanfiction could be about Naruto characters attending the school in High School DxD. For example, Naruto's positive and determined attitude might clash with the more complex social and power dynamics in the DxD world. He could make new friends or even rivals among the devils, angels, and fallen angels.
One idea could be that Ben Tennyson somehow gets transferred to the world of High School DxD. He has to keep his alien forms a secret while dealing with the devils, angels, and fallen angels in the school. Maybe his Omnitrix could be misinterpreted as some kind of powerful devil device.
One possible fanfiction could be about Naruto characters somehow ending up in the world of High School DxD. Maybe Naruto's skills in combat and his determination would make him a formidable opponent in the battles that often occur in the High School DxD universe. He could form interesting alliances or rivalries with the characters there.
A fanfiction could focus on Naruto's training regime influencing the characters in High School DxD. His intense physical and mental training could inspire the students at the school. They might start incorporating some of his training methods, like running up trees or on water, to improve their own strength. And Naruto could also learn from their magic-based training and combine it with his chakra control for new and powerful techniques.
A fanfiction might explore how the power of the Excalibur in High School DxD would interact with Naruto's chakra. Since the Excalibur is a powerful holy weapon, it could have some interesting reactions when in the presence of Naruto's unique chakra, which is different from the magic in the High School DxD world. For example, it could either enhance or nullify certain abilities depending on how the author writes it.