Great Red in such a fanfiction might be a sort of guardian or a threat depending on how the author writes it. If it's seen as a guardian, it could be protecting the new world that combines elements of Naruto and High School DxD from some greater evil. However, if it's a threat, it could be trying to consume the chakra and magic in this new world to become even more powerful.
Well, in a Naruto - High School DxD fanfiction, Great Red could be a super powerful entity that disrupts the balance. Maybe it has some connection to the tailed beasts in Naruto. For example, its power could be on a similar scale to the combined might of all the tailed beasts, causing all sorts of chaos in the crossover world.
In this type of fanfiction, Great Red could also be a mystery that the characters from both Naruto and High School DxD have to figure out. The ninjas from Naruto might approach it with their combat skills and jutsu, while the devils and other beings from High School DxD could use their magic and unique abilities. The exploration of Great Red's nature and its place in this combined universe could be a really interesting plot point.
Well, a fanfiction like this could be really interesting. One way it could work is by having a character from Naruto world somehow end up in the High School DxD universe and interact with the archangels there. Maybe Naruto himself could gain some new powers related to the angelic realm in this crossover. He could learn about different hierarchies of angels which are very different from the ninja system he's used to.
A Naruto - High School DxD fanfiction with the concept of immortality could start with Naruto being summoned to the DxD world by an unknown force. Since he's immortal, he doesn't fear death like many in the DxD world do. This could lead to him taking on more dangerous quests or getting involved in the wars between the different species. He could also use his immortality to experiment with different powers and techniques in the DxD world without the risk of dying, which would make him a very formidable and unpredictable character.
One idea could be a crossover where Naruto is somehow transported to the world of High School DxD. He meets Gabriel, and they team up to face a common threat. Maybe a powerful devil or a new, unknown enemy. Naruto's ninja skills could be a great asset in the battles of the DxD world.
One idea could be that Naruto is somehow transported to the world of High School DxD and meets Moka. He could use his ninja skills in the battles that take place in the DxD world. Maybe he teams up with Moka to fight off common enemies.
Yes, there are likely fanfictions that combine the two universes in a non - sexual way. Many fans enjoy creating crossovers that focus on adventure, friendship, or the characters facing new challenges together. For example, they might write about Naruto characters ending up in the High School DxD world and having to adapt to its unique rules and magic systems while still maintaining their own ninja skills and values.
Another idea is that Naruto is reborn in the High School DxD world as a half - dragon due to the influence of the Dragon God. He then has to navigate the complex social and power structures of the DxD world while also hiding his true identity at first. As he discovers more about his new powers and the world around him, he gradually becomes a key figure in the battles and politics of the DxD world.
One possible storyline could be that Naruto, with his unique skills and positive attitude, enrolls in the high school from High School DxD. He might form an unlikely friendship with some of the characters there, like Issei. Together, they could face off against common enemies, with Naruto teaching Issei some of his ninja techniques, adding a new dimension to the battles in the High School DxD universe.
Firebrand could be a student in the High School DxD setting who has a strange connection to the Naruto world. Maybe they have dreams or visions of the Naruto world and start to develop ninja - like abilities in the High School DxD world. This could lead to them being an outcast at first, but as they grow in power, they become a key figure in protecting the school from threats that are both from the High School DxD universe and potentially threats that have some connection to the Naruto world.
There could be an interesting story where the Red Dragon Emperor's powers are introduced into the Harry Potter universe. Maybe he could attend Hogwarts and cause quite a stir among the students and faculty. His unique abilities might be seen as both a threat and an asset in the wizarding world.
Naruto characters could be in awe of the devils and angels in the High School DxD world. When it comes to Great Red, Naruto himself might see it as a new and powerful force to either befriend or fight. He could try to use his Rasengan or other jutsu against it if it poses a threat.