Another approach could be to have Naruto's shadow clones play a major role in the DxD world. Since he can create so many clones, they could be used for various tasks like spying on the different factions in DxD. Also, Naruto's ability to befriend people might lead to some interesting interactions with the characters in DxD, like making friends with Rias and her peerage.
One idea could be to create a fanfic where Naruto is somehow transported to the world of High School DxD. He could bring his unique ninja skills and chakra system. Maybe he teams up with Issei to fight against a common enemy. For example, a powerful devil or fallen angel that threatens both the ninja world and the DxD universe.
A third idea is to explore how Naruto's jinchuriki powers would be perceived in the DxD world. The demons in DxD might be both intrigued and a bit afraid of the power of the tailed beasts inside Naruto. This could lead to a complex power dynamic where Naruto has to balance his relationships with different species in DxD while also dealing with his own inner demons, so to speak.
The best chapter pointer here is Chapter 48, "All the Bitter Teas Have Been Taken Away". It opens with He Yun felt guilty for initially ignoring Jiang Li on purpose, and with... and closes on Besides, everyone's phones will be replaced with special smartphones....
If you want the clearest chapter reference, go to Chapter 18. Early on, In the corner, a girl in a black dress sat quietly, holding a glass of...; later, the chapter leans on Her serene yet cold temperament, along with her exquisitely beautiful....
Look to Chapter 81 for the clearest answer. It begins with Qi Tianyu, who chose curry beef rice, received a piece of curry and a..., keeps building through Shu Yan was relatively lucky, she got a bundle of noodles and a bag of..., and lands on The summer on the Southwest Plateau is no joke;
A practical answer is Chapter 55, because it turns the idea into a concrete scene. The chapter opens with Su Yinwan hadn't expected that, in just one day, Jiang Li's reputation had..., adds pressure through This person was even a top gaming streamer with tens of millions of fans,..., and ends on.
A practical answer is Chapter 15, because it turns the idea into a concrete scene. The chapter opens with Jiang Shixu woke up from those nightmares filled with blood and darkness,..., adds pressure through Jiang Shixu's mind was starting to cloud, but for some reason, when he..., and ends on Since.
Look to Chapter 85 for the clearest answer. It begins with Facing everyone's skepticism and curiosity, Jiang Li explained fluently:..., keeps building through The tomatoes are grown by them, and the eggs are also from their..., and lands on This fresh and vibrant flavor blended perfectly..
Look to Chapter 23 for the clearest answer. It begins with Although Jiang Li exerted very little strength, Jiang Yan instantly felt..., keeps building through The pain twisted his face grotesquely as he dove headfirst into the sofa., and lands on However, just as she buried herself in the study.
If you want the clearest chapter reference, go to Chapter 47. Early on, Qi is actually second???] [Did the production team make a mistake?; later, the chapter leans on Isn't Qi supposed to be first?] [So who's first?.
The best chapter pointer here is Chapter 74, "Ordinary People". It opens with Having seen Jiang Li's ID before, he knew that this person named Shiguang... and closes on The man's phoenix eyes narrowed slightly, he looked at the girl sitting....
Chapter 40 is the strongest chapter-level answer because it starts from [Jiang Li claims she copied this herself? and follows through on The handsome guys on this show are so difficult to deal with..