In this fanfic, the power - up concepts can be very interesting. Since both Naruto and DxD have different power systems. A character might gain new powers by combining the chakra system with the sacred gears in DxD. This could lead to unique abilities that we haven't seen in either of the original stories, like a sage - mode enhanced by a sacred gear's power.
One interesting concept could be the fusion of the Naruto and High School DxD universes. For example, seeing how Naruto's ninja skills would interact with the devil - based powers in DxD. Maybe Naruto characters using their chakra in the DxD world to fight against devils or angels in new and unexpected ways.
It could be Naruto himself. He has a strong personality and a lot of potential for growth in a new world like DxD. His journey to adapt to the DxD universe and its rules would be very engaging.
Some fanfics might explore the backstory of the nekomata in the Naruto setting. It could be that the nekomata was once a normal cat that was experimented on by a mad scientist - like ninja. The transformation into a nekomata gave it great power but also a lot of confusion and fear. The story could then follow its journey to understand its new self and find its place in the Naruto world.
One interesting concept could be alternate universes where the characters have different powers or relationships. For example, a fanfic might explore a world where Issei has angelic powers instead of his usual devil powers. Another concept could be character crossovers, like bringing in characters from other anime into the Highschool DxD universe.
The fact that it can expand on the Naruto universe. For example, fanfics can explore different relationships between characters that were not fully developed in the original. Like a deeper bond between Naruto and Gaara.
The cultural clash is really interesting too. Naruto comes from a world with a very different culture compared to the DxD world. Adding Devil Fruits into the mix makes it even more complex. For instance, Naruto's values of loyalty and hard work might interact in unexpected ways with the more morally ambiguous elements of the DxD world and the power - hungry nature often associated with Devil Fruit users.
One interesting concept could be the fusion of Naruto's ninja abilities with the supernatural elements from High School DxD. For example, imagine Naruto using his shadow clone jutsu in the middle of a devil - angel battle in the DxD universe. It would add a whole new dynamic to the battles there.
One interesting concept could be the combination of different power systems. For example, how the ninjutsu from Naruto might interact with the magic in DxD. Maybe a character could use shadow clones to perform a complex magic spell simultaneously. Another concept could be the crossovers of characters. Picture Naruto characters in the DxD world, like Naruto himself being in the middle of a devil - angel - fallen angel conflict. It could lead to really unique story developments.
Another concept is the character relationships. In a 'dxd issei crossover fanfic', we might see Issei form new alliances or rivalries. He could meet characters with similar or completely different personalities and values, which would lead to some really engaging character - driven storylines. For instance, if he crosses over into a world with more morally ambiguous characters, it could force him to reevaluate his own beliefs.
The power dynamics can also be really engaging. Maybe in 'annihilation maker dxd fanfic', the way powers are used and developed is different. Some characters could gain new abilities or find different ways to utilize their existing ones. This can lead to intense battles and strategic planning within the story.