The plot could also involve Naruto being mistaken for a new type of devil or a strange being in the Highschool DxD world. His chakra could be seen as a very unique power source. He might have to go to the high school in the DxD world and get into all kinds of adventures, like dealing with the pervy situations that Issei often finds himself in, but with his own Naruto - style humor and strength.
Naruto would probably be really friendly and try to make friends right away. He might be a bit confused at first about the different species in Highschool DxD, but his open - mindedness would help. He could bond with Issei over their shared love for the opposite sex in a very comical way. For example, Naruto would be more innocent about it compared to Issei.
One idea could be a new character who is a transfer student with a unique Sacred Gear that no one has seen before. This character could disrupt the power balance in the school and create new alliances and rivalries.
In this fanfic, Naruto could bring his sense of justice to Sona's side. Since Naruto is always about protecting his friends and doing what's right, he could inspire Sona and her followers. His chakra could be an interesting element in the world of devils and angels. He might even find a way to use his chakra to enhance the abilities of Sona's peerage members.
In a fanfiction where Naruto goes to Highschool DxD, he could introduce new concepts of chakra to the world. This would be really fascinating as the characters in DxD might try to incorporate it into their own powers. Naruto could also be a bit of a fish out of water, not fully understanding the social norms and hierarchies in Highschool DxD at first. But his kind heart would help him navigate through it all, and he'd end up changing the school environment in a positive way with his unique personality.
One popular theme is power - ups. In both Highschool DxD and Campione, power is a significant aspect. Fanfictions often explore characters getting new and stronger powers, and how they use them. For example, in Highschool DxD, a fanfic might focus on Issei getting a new form of his Boosted Gear.
It might be a story where the concepts from Naruto and Highschool DxD are mashed up. For instance, the power systems could be combined. Naruto's chakra and the magic or sacred gears in Highschool DxD could interact in interesting ways. And perhaps the characters from both series form new alliances or rivalries based on their different abilities and goals.
A possible scenario is that Ravel teams up with Naruto to fight a common enemy. Ravel's magical abilities and Naruto's ninjutsu would make for an interesting combination. They could learn from each other's fighting styles during their battles, and their friendship could grow as they face challenges together.
The plot might revolve around Naruto's Juubi powers disrupting the balance in the Highschool DxD universe. This could lead to him having to either hide his powers or learn to control them in a new way. He might get involved in the Rating Games, using his ninja skills and Juubi - enhanced abilities to compete. And of course, there would be some sort of character development as he adapts to this new world.
Well, in a 'Naruto x Greyfia Highschool DxD' fanfiction, perhaps Naruto is a new transfer student in the Highschool DxD. Greyfia could be a popular student there. Naruto's positive and energetic attitude might attract Greyfia's attention. They could start off as friends and gradually develop a deeper relationship. Maybe they get involved in the supernatural battles of the DxD world together, with Naruto using his Rasengan and other jutsu while Greyfia uses her demonic powers. And as they spend more time together, they learn from each other's worlds and values.
One possible plot could be that Naruto is somehow transported to the Highschool DxD universe and meets Gabriel. They might team up to face a common threat that is endangering both the ninja world and the supernatural world of Highschool DxD. Naruto's unique skills as a ninja could be combined with Gabriel's angelic powers in an epic battle against evil forces.