Well, it could be about Ichigo having some super - transcendent powers that he has to hide in the High School DxD world. Maybe he's a new student there and his powers start to disrupt the normal balance of the supernatural elements in the school.
In 'Twisted Fates', the plot twist is that the powers of Ichigo and a certain devil in High School DxD get merged accidentally. This leads to a new form of power that no one expected. It causes a huge shift in the power balance and makes both the allies and enemies of the characters scramble to adjust to this new situation. This fanfiction then delves into how they all cope with this unexpected development.
One great Ichigo High School DxD fanfiction is 'The Hybrid's Journey'. It combines the unique elements of both Ichigo's powers from Bleach and the exciting world of High School DxD. The story follows a new character who has a mix of both universes' traits and how they navigate through the challenges in this combined world.
He could fit in as a mysterious new student. His transcendent powers would set him apart from the rest. He might initially be seen as a threat by some of the factions in the school.
The story mainly follows Issei Hyodo, a high school student who gets killed on his first date and is later resurrected as a devil. He then becomes part of the Occult Research Club at his school. There, he gets involved in various battles against other supernatural beings, all while trying to become stronger and also dealing with his new devilish desires and relationships with his female comrades.
Well, there are prequel novels that offer background on some of the characters and events. Also, there are companion novels that explore additional adventures and story arcs within the same world.
In a Naruto and High School DxD fanfiction, there could be a scenario where the protagonists of both stories meet in a neutral dimension. Issei from High School DxD might be intrigued by Naruto's ninja skills and determination. Naruto, in turn, could be curious about Issei's Sacred Gear. They could start training together, sharing their knowledge and skills, and ultimately have to face a common enemy that threatens both their worlds.