A possible blend in the fanfiction could be through a magical or technological device. Maybe a scientist in Highschool DxD creates a device that can open portals to other universes, and Naruto's world is one of the destinations. When Naruto arrives, he discovers that there are elements related to Beelzebub there. The device could malfunction and start to merge the three universes in unexpected ways. This would force the characters to adapt to the new situation, with Naruto using his ninja training to survive, the Highschool DxD characters using their social and magical skills, and those related to Beelzebub using their demonic powers to deal with the chaos.
Well, one way is through character exchanges. Imagine a character from Naruto like Naruto himself ending up in the Highschool DxD universe and meeting Leviathan. He could introduce his ninja skills to that world and also learn about the devil powers. Another way is to have a common enemy. For instance, a new threat that can only be defeated by combining the unique powers from all three, like the Rasengan combined with a Highschool DxD power against an enemy threatening Leviathan.
One way is through the power system. The Susanoo's power could be compared or combined with the powers in Highschool DxD. Naruto could bring his ninja way of thinking into the Highschool DxD world. For instance, his idea of never giving up could inspire the Highschool DxD characters. And in terms of the world - building, the fanfic could have Naruto's world of ninjas and the Highschool DxD's world of demons and angels co - exist. The Susanoo could be seen as a new and fearsome power in the Highschool DxD world.
One way is through character crossovers. For example, a character from Fate Stay Night could end up in the Highschool DxD universe or vice versa. They could then interact with the native characters, creating new and interesting storylines. Another way is to combine the magic systems. The magic in Fate Stay Night is very different from the supernatural powers in Highschool DxD, and blending them could lead to unique and exciting plot developments.
If Kitsune Naruto was in Highschool DxD fanfiction, it could change the power balance. Naruto is already a very powerful character from his own series. His Kitsune powers, like the nine - tailed fox's chakra, are extremely potent. In Highschool DxD, this could make him a major player. He might not be as interested in the whole devil - angel - fallen angel conflict as the original characters, but his presence would force all the parties to take notice. His unique abilities would also mean that he could teach the other characters new ways of fighting or using their powers, which would have a big impact on the overall story.
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.
Well, it could be a really wild and interesting mix. Imagine Naruto's ninja skills in the world of Highschool DxD with all its demons and magic. And then throw in Beelzebub's characteristics. Maybe Naruto could use his Rasengan against the devils in Highschool DxD while having some of Beelzebub's powers or traits. It could lead to some really epic battles and unique character interactions.
Naruto fanfictions often add new jutsus or powers to the characters, thus expanding the power system of the universe. For instance, a story might introduce a new type of Sharingan ability. In Highschool DxD, fanfictions can expand on the idea of the Sacred Gears. A fanfic like 'The Sacred Gear Evolution' shows how these gears can have even more complex and powerful forms, which enriches the Highschool DxD universe.
Often, the storylines blend by having characters from Naruto end up in the Highschool DxD world. For example, Naruto might be summoned there by some sort of magic accident. Then, he has to navigate this new world full of devils, angels, and other supernatural beings while still having his ninja mindset and skills.
Well, first of all, the writers often take the unique elements from each universe. From Naruto, it's the ninjutsu, kekkei genkai, and the concept of the ninja villages. From Highschool of the Dead, it's the zombie apocalypse and the school environment. They then find ways to make these elements work together. Maybe a character with a Sharingan from Naruto can use its powers to detect zombies from afar. Also, they might use the character relationships. A Naruto character could form a team with some Highschool of the Dead survivors to face the challenges together. And they might also play with the different values of the two universes. For example, the loyalty in Naruto and the survival instinct in Highschool of the Dead.
Naruto would be different in this fanfiction in many ways. Firstly, his appearance might change slightly to fit the more modern and different aesthetic of the Highschool DxD world. His clothing could be a mix of his ninja gear and the school uniform of Highschool DxD. His power would also have new applications. For example, his shadow clone jutsu could be used in creative ways in the battles and social situations in Highschool DxD. His character would grow as he learns about the new races and abilities in the Highschool DxD world, and he might start to see his own powers from a different perspective. He'd be more of a bridge between the two worlds, bringing his ninja values and adding them to the mix of the Highschool DxD universe.