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.
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 storyline could be that Naruto, as a yokai, has to hide his true identity in the Highschool DxD world. He might get involved in the power struggles between different factions while also trying to fit in at school. Another could be that he uses his yokai powers to help out the main characters in Highschool DxD, like Issei, in battles against their enemies.
One possible plotline could be Naruto being transported to the Highschool DxD world and having to adapt to its unique rules and social hierarchy. He might use his ninja skills to rise through the ranks in the school. Another could be that Naruto's presence disrupts the existing power balance in the DxD world, leading to various conflicts and alliances. Maybe the devils and angels in the DxD world are intrigued by Naruto's power and try to either recruit him or eliminate him.
Well, one possible plotline could be Naruto, in the form of a hound, somehow gets transferred to the Highschool DxD world. He might have to deal with the different factions and powers there while still retaining some of his Naruto - like abilities.
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.
Maybe Venelana has some connection to a powerful artifact in the Naruto world. Naruto and Venelana then have to embark on a journey to find this artifact before it falls into the wrong hands. Along the way, they learn about each other's cultures and powers.
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.
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.
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 possible plotline could be that Naruto is transported to the Highschool DxD world and immediately notices Rias's overbearing attitude. He decides to oppose her and starts to gather allies among the other students and characters who are also fed up with her ways. As a result, a power struggle ensues between Naruto and Rias.