The storyline would be different in that Naruto could use the Rinnegan's powers to form alliances in a unique way. For example, he could use his ability to see chakra or the equivalent energy in the DxD world to identify those with hidden potential or motives. His presence with the Rinnegan might also attract different factions. Some might want to use his power, while others might fear it. This would create a whole new web of relationships and conflicts in the Highschool DxD fanfiction setting.
If Naruto had the Rinnegan in a Highschool DxD fanfiction, it would also change the way the characters interact with him. The devils in Highschool DxD are used to a certain set of powers and rules. Naruto's Rinnegan - with its abilities like the Six Paths techniques - would be something completely new. His classmates at the high school might be in awe or fear of him. And he'd have to navigate the social and political aspects of the DxD world while also dealing with his new - and extremely powerful - eyes.
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.