Another way is through their own sense of identity. Despite being an orphan, they have their own values and beliefs. In the fanfiction, they can use these to navigate the complex moral landscapes of both worlds. In High School DxD, they can decide for themselves which side to align with based on their own understanding of right and wrong, influenced by Naruto's teachings of protecting friends and standing up for what's right. They can also bring their Naruto - inspired fighting spirit to the battles in High School DxD, showing that their orphan status doesn't make them weak but rather gives them a unique strength.
The orphan could rely on their adaptability. Since they are used to being alone, they might be more open to learning the new rules of both worlds. In the Naruto world, they might have learned to be resourceful, and they can apply that in High School DxD. For example, using their knowledge of chakra to understand and maybe even manipulate the magic in High School DxD.
They could also use their experiences as an orphan to form unique relationships. In High School DxD, they may find that some characters are sympathetic to their orphan status. And in the Naruto world, they might have already had some bonds with other outcasts. By combining these experiences, they can build a support network in both worlds. They may befriend some of the more understanding devils or angels in High School DxD, and in Naruto, they could have friends among the ninja who also had difficult upbringings.
Typically, they use some sort of magical or dimensional rift to merge the two worlds. For example, Naruto could be sucked into a portal that leads him to the High School DxD universe. Or, it could be a more complex plot device like a powerful villain trying to combine the two worlds for their own gain.
One way is through the concept of power transfer. For instance, a character from Naruto could accidentally gain the power of a devil in High School DxD and have to figure out how to control it. This would lead to some really cool action scenes as they struggle with the new power. Another way is through cultural exchange. The shinobi culture from Naruto could be introduced to the High School DxD characters, creating some interesting interactions.
The fanfiction could also explore how the values from Naruto's world, such as perseverance and friendship, play out in the often morally - grey world of High School DxD. The orphan might try to bring a more positive and Naruto - esque attitude to the relationships between the different species in High School DxD. They could form unlikely alliances with devils, angels and fallen angels based on their own understanding of loyalty and comradeship from Naruto's story.
One way is through the power systems. Naruto's chakra could interact with the magic and powers in High School DxD. For instance, a character from High School DxD might be fascinated by Naruto's ability to use chakra and it could be a starting point for a relationship in the mass harem. Another aspect could be the cultures. The shinobi culture of Naruto's world is very different from the high school and supernatural culture of High School DxD. This contrast could create interesting situations in the fanfiction.
The power systems might also clash. In the Naruto world, power often comes from training and mastering one's own internal energy. In High School DxD, it's more about the power of the Devils, Angels, and Fallen Angels. So when Naruto enters the DxD world, his idea of power through hard work might be at odds with the more innate powers of the DxD characters. He could try to teach them his ways, or they could try to convince him that their powers are superior.
Another possibility is that there is a tournament that spans multiple universes. Naruto is selected to represent his world, and Rias volunteers or is chosen to represent the High School DxD world. They meet at the tournament grounds. At first, they might be a bit suspicious of each other, but as they see each other's skills and determination in the battles, they start to respect and eventually become friends, working together to win the tournament for their respective worlds.
Yes, there are some. You can start by looking on fanfiction platforms like FanFiction.net or Archive of Our Own. Some authors create crossovers where Naruto characters interact with the High School DxD universe in a platonic or adventure - based way. For example, they might have Naruto and his friends visit the DxD world to help with a demon - related problem, without any inappropriate content.
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.
Another approach is to mix the power systems. In fanfiction, the chakra from Naruto could be related to the power of the devils or other beings in High School DxD. For instance, the tailed - beast chakra could be equivalent to a powerful devil's power source. Characters from both universes could then try to learn about and utilize the other's power system. This would create a lot of interesting scenarios where they have to train together or compete to see who has the stronger power.
One way to combine them could be by having Naruto characters enter the world of High School DxD. For example, Naruto with his determination and unique abilities could interact with the devils and other supernatural beings in the DxD world. Maybe he'd form an unlikely alliance or even compete in the Rating Games.