One possible plot could be that Naruto, with his unique ninja skills, is transferred to the Highschool DxD world. He could form an unlikely alliance with the main characters there. Maybe he uses his shadow clone jutsu to help out during some of the school's chaotic events or battles against the devils and fallen angels, adding a new and unexpected element to the Highschool DxD's power dynamics.
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.
Issei is a must - include character. His growth and relationships in the original series can be further explored in a hybrid fanfiction. For example, if he had a hybrid friend or love interest, it could change the dynamics of his character development.
A fanfiction could center around a hybrid who is trying to bridge the gap between the different supernatural groups in the highschool dxd universe. They could start a club or an organization that promotes peace and understanding among devils, angels, and other beings. This would involve a lot of character development as they face opposition from traditionalists in each group who don't want things to change.
Issei is often a central character in such fanfiction. His growth and development in the original series make him a great base to build on in dragon hybrid fanfiction. Writers might explore how he would interact with a dragon hybrid character, either as an ally or a potential rival.
One idea could be that Naruto is somehow transported to the world of Highschool DxD. He could use his ninja skills and chakra in the new world, maybe even teach some of the characters there a thing or two about combat. For example, he could show Issei how to better control his power using chakra control techniques.
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.
One idea could be an OC who is a hybrid of a devil and a fallen angel. The story could revolve around their struggle to find a place in both worlds. They might face discrimination from pure - blooded devils and fallen angels alike, but also discover unique powers that come with their hybrid nature.
One idea could be a dragon hybrid character who is trying to hide their true nature in the high school setting of Highschool DxD. They constantly have to struggle with the urges and powers that come with being a dragon hybrid while also dealing with the typical high school drama.
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.