In fanfiction, such a betrayal could occur due to power struggles. Maybe Rias sees Naruto as a threat to her position in the Highschool DxD world. She might fear his growing power and influence, which could overshadow her own. So, in order to maintain her status, she betrays him.
Perhaps Naruto would try to find allies among the outcasts in the Highschool DxD world. Since he has been betrayed, he would understand the feeling of being alone and might reach out to those who are also on the fringes of society. He could form a new group that challenges the existing power structures in the Highschool DxD universe, using his unique abilities and his unwavering will from the Naruto world.
Naruto would likely become very distrustful. After being betrayed by Rias, he would find it hard to trust anyone else in the Highschool DxD world. This could isolate him and make his journey much more difficult as he would be on his own without allies.
One interesting 'Betrayed Highschool DxD Fanfiction' could be where the main character is betrayed by his friends in the Occult Research Club and has to find a new path on his own. Maybe he teams up with some unexpected allies from the underworld.
Issei is often a central character in these fanfictions. Since he is the main protagonist in the original series, his relationships and potential betrayals are explored. For example, a situation where his friends or allies in the Occult Research Club turn against him for some reason, like jealousy over his growing power or a misunderstanding about his actions.
One interesting plot could be where a main character is betrayed by a close friend within the Highschool DxD universe. For example, a devil might be betrayed by another devil who has a hidden agenda related to power or territory. This could lead to intense battles and power struggles as the betrayed character tries to seek revenge and regain their status.
Naruto's powers are quite different from those in Highschool DxD. His chakra - based abilities like the Rasengan would be completely new to the Highschool DxD world. While the characters in Highschool DxD have their own unique powers such as devil's power, angelic abilities and sacred gear. Naruto's ability to quickly create multiple clones would give him an edge in combat or in situations where numbers matter. His stamina and endurance, which are enhanced due to his ninja training, would also be a great advantage.
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.
One possible fanfiction could involve a crossover where the characters from Highschool DxD and Naruto meet in a unique world. Yasaka, being a powerful figure in the Highschool DxD universe, might interact with Naruto characters. For example, she could form an alliance with Naruto to fight against a common enemy that somehow threatens both of their worlds. Maybe a group of rogue ninjas from Naruto's world team up with some rogue devils from Highschool DxD.
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.