Naruto could appear in Highschool DxD fanfiction if there is a plot device like a forbidden scroll or a magical artifact that has the power to transport characters between different fictional universes. A curious character in the Highschool DxD world might accidentally activate it and bring Naruto into their world. Also, some fanfictions like to play with the idea of alternate realities. So, in an alternate reality, the universes of Naruto and Highschool DxD could merge, allowing Naruto to be a part of the Highschool DxD story.
In a Highschool DxD fanfiction, Naruto might appear if the author wants to create an interesting mash - up. It could be that Naruto is on a new mission and somehow ends up in the Highschool DxD world. For example, he could be chasing after a rogue ninja who has found a way to hide in that different realm. Or perhaps, the fanfiction writer just wants to see how Naruto's unique abilities, like his shadow clones or Rasengan, would interact with the magic and powers in the Highschool DxD setting.
Well, it could start with a portal opening up between the two universes. Yasaka could be the first to sense it and investigate. She then meets Naruto and they start to communicate through some kind of magic or chakra - based translation. As for the Highschool DxD characters, they could follow Yasaka's lead. They could then all work together to close the portal which is causing some sort of instability in both worlds.
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 way could be that Naruto's skills and values from his own world clash and then blend with the supernatural elements in Highschool DxD. For example, his strong sense of justice might lead him to oppose some of the more chaotic or immoral actions in the DxD world. And his ninja techniques could be a new and interesting addition, like using shadow clones in battles against devils or fallen angels. Kurama could also play a role, perhaps his chakra influencing the power dynamics in the DxD setting.
Yes, he can. In fanfiction, the writer has the creative freedom to cross different universes. Naruto could be a father in a Highschool DxD setting perhaps through some sort of interdimensional travel or magical event. Maybe he's brought into the Highschool DxD world and starts a family there. It's all about the wild and creative ideas that fanfiction allows.
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.
A possible way for their worlds to merge in fanfiction is through a reincarnation plot. What if some of the Naruto characters were reincarnated in the Highschool DxD world? Naruto himself could be reborn as a devil or an angel. This would completely change the power balance and relationships in the Highschool DxD world. Rias would have to deal with this new Naruto, who still has his ninja spirit but now has to adapt to the rules and powers of the new world.
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 possibility is that a writer might create a backstory where Naruto's unique chakra or abilities are needed to save Kunou's mother from a great danger. In the process, a bond forms between them and through some unorthodox means, Naruto becomes the father. Another aspect could be that in the fanfiction world, there are new rules and the author wants to explore the combination of Naruto's ninja world elements with the devil - based world of 'Highschool DxD' to make Naruto Kunou's father.
In a Sharingan Naruto Highschool DxD fanfiction, the Sharingan could also play a role in terms of illusions. Imagine a scenario where the character uses Sharingan - based illusions to deceive the enemies from both worlds. They could make a Highschool DxD devil believe they are in a completely different environment like a dangerous Naruto - style forest filled with traps. And for Naruto characters, they could be made to see illusions of their worst nightmares or false threats from the Highschool DxD world, which would make for some really intense and engaging storylines.
In fanfiction, anything can happen. The author might have created a crossover concept where Naruto's abilities are combined with elements from Highschool DxD. Maybe it's a result of some magical or scientific experiment in the fictional world of the fanfic. It could also be a unique power that Naruto acquires during his adventures in the Highschool DxD universe.