One way to combine them creatively is to have Naruto characters with Rinnegan powers in a Highschool of the Dead - like scenario. For example, the Rinnegan could be used to detect zombies from afar, similar to how it can sense chakra in Naruto. The high school setting could be filled with Naruto - style ninjutsu battles against the undead.
A plot idea could be that a group of students suddenly develop Rinnegan powers during a zombie outbreak in their high school. They must then figure out how to use these powers to not only survive but also find a cure. Another idea is that a Naruto - like character from another dimension arrives in the Highschool of the Dead world with Rinnegan and tries to teach the survivors ninjutsu to fight the zombies.
A story could revolve around a Naruto character with the Rinnegan who is mistaken for a new type of supernatural being in the Highschool DxD world. As they navigate this new environment, they might have to hide their true identity at first. But as the story progresses, they could reveal their powers and form alliances with some of the factions in DxD. They might also introduce some ninja concepts like chakra and jutsu to the DxD characters, which could change the power dynamics in that world.
Naruto's experience in dealing with tough opponents in his own world would help him in the zombie - filled Highschool of the Dead. He would be able to quickly analyze the situation, figure out the weaknesses of the zombies, and come up with effective plans. His friendship - first approach might also lead to some interesting relationships with the other characters in this new and dangerous world.
As a transfer student, Naruto with the Rinnegan would change the balance of power in the school. He could be a target for some groups who want to study or steal his power. At the same time, he could be a great asset to the school in protecting it from external threats. His Rinnegan - which gives him abilities like seeing the chakra flow of others - would be very useful in detecting hidden enemies or spies within the school. This would create a lot of drama and action in the fanfiction.
One possible aspect of such a fanfiction could be the combination of Naruto's ninja skills in the zombie - infested world of Highschool of the Dead. For example, Naruto's shadow clone jutsu could be used to distract the zombies while the characters from Highschool of the Dead search for supplies or a safe place. His ability to move quickly and stealthily like a ninja would also be a great advantage in that dangerous setting.
An OC (Original Character) in a Highschool DxD fanfiction having the Rinnegan could be an extremely powerful and unique addition. The Rinnegan, from the Naruto universe, brings a whole set of abilities like the Six Paths powers. In the context of Highschool DxD, this OC could use these powers in various ways. For example, the ability to see chakra could be translated into seeing the magical energy in the DxD world. They could use the gravitational powers of the Rinnegan to manipulate the environment during battles against devils, angels, or fallen angels. It would make for a very interesting and overpowered character in the Highschool DxD fanfiction setting.
Well, first of all, the writers often take the unique elements from each universe. From Naruto, it's the ninjutsu, kekkei genkai, and the concept of the ninja villages. From Highschool of the Dead, it's the zombie apocalypse and the school environment. They then find ways to make these elements work together. Maybe a character with a Sharingan from Naruto can use its powers to detect zombies from afar. Also, they might use the character relationships. A Naruto character could form a team with some Highschool of the Dead survivors to face the challenges together. And they might also play with the different values of the two universes. For example, the loyalty in Naruto and the survival instinct in Highschool of the Dead.
Well, if Naruto had the Rinnegan in the Highschool DxD world, the power dynamics would change drastically. Naruto's abilities with the Rinnegan could make him a dominant force in the battles against the devils and other supernatural beings. He might introduce new jutsu styles that could shock everyone in the DxD universe. Maybe he'd use his Rinnegan to quickly analyze the powers of his opponents and come up with strategies on the fly.
Yes, there are likely some available. You can try searching on fanfiction websites like FanFiction.net or Archive of Our Own. Just type in the relevant keywords, and you might find some interesting stories that combine the elements of Naruto, a godlike Naruto in this case, and the Highschool of the Dead setting.