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.
Well, in the realm of fanfiction, anything is possible. Naruto being a father in a Highschool DxD fanfiction could be due to a complex plot device. Imagine a situation where the two universes collide and Naruto finds himself in the Highschool DxD world. His ninja skills and values might make him stand out, and he could end up forming relationships that lead to him becoming a father. This could involve him mentoring and eventually having a family with one of the characters, adding a whole new dynamic to the story.
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 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.
In fanfiction, anything is possible. Naruto has his powerful jutsu like Rasengan and Shadow Clone Jutsu. If he were in the Highschool DxD universe, he might use his speed and surprise factor. Maybe he could catch Riser off - guard and land a fatal blow with a Rasengan. However, Riser also has his own set of powers in the Highschool DxD world. So it would be a very interesting and intense battle if written well in a fanfiction.
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.
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.
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.
He would be a very protective father. Given Naruto's own experiences growing up without parents and his strong will to protect his loved ones, he would be extremely vigilant in safeguarding his family in the Highschool DxD fanfiction.
One possible plot could be that the characters from Naruto and Highschool DxD somehow end up in the same universe as the Khaos Brigade. Maybe Naruto characters are sent to the Highschool DxD world to help fight against the Khaos Brigade's evil plans. They could bring their unique ninja skills, like Naruto's shadow clones or Sasuke's sharingan, and team up with the devils and other beings in the Highschool DxD world to protect it.
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.
If Naruto is Kunou's father, it would mean a whole new set of powers for Kunou. Combining Naruto's chakra - based powers with the devil - like abilities in 'Highschool DxD', Kunou could be extremely powerful. For example, she might be able to use Naruto's Rasengan technique along with her own devil powers.