The plot could be that Naruto is somehow transported to the Hellsing universe. He starts off as an outsider but quickly proves his worth. His rasengan could be adapted to be effective against vampires, perhaps by infusing it with holy water or some other vampire - weakening element. Naruto's presence could also introduce a new dynamic to the relationships within the Hellsing organization, and he might even form an unexpected bond with Seras Victoria as they both have a strong sense of loyalty and a desire to protect the innocent.
Well, in such a fanfiction, Harry Potter might bring a new perspective to the Hellsing crew. He comes from a world where magic has different rules and ethics. His presence could lead to some internal conflicts within Hellsing as they debate whether to trust his 'alien' magic. Also, Harry might be shocked at the extreme measures Hellsing takes against vampires and other supernatural beings, and try to find a more 'humane' solution while still protecting humanity.
One possible plot is that there is a breach between the Naruto universe and the Hellsing universe. This causes chaos as demons from Hellsing start to invade Konoha. Naruto, being the hero, tries to figure out how to stop them. Alucard arrives, not entirely as an ally at first. But as they both realize the common threat, they join forces. Naruto learns about the different nature of the enemies from Alucard and adapts his ninja skills accordingly.
One possible plot could be that Naruto and his team are sent to the Hellsing universe on a mission. They encounter Alucard and his group. Naruto, with his ninja skills and strong will, might initially be seen as a threat by the Hellsing crew. But as they learn about his world and his fight for peace, they start to work together. Maybe Naruto tries to understand Alucard's vampiric nature and in turn, Alucard is intrigued by Naruto's chakra and jutsu. Together, they could face a new threat that is endangering both their universes.
Well, in this fanfiction, Naruto could join Esdeath in her military campaigns. Since Naruto has his own set of powerful jutsu, he could be a great asset. The plot could revolve around how Naruto adapts to the new world's rules and politics. He might be shocked by the harshness of Esdeath's world but still tries to bring some of his positive values. They could form an unlikely alliance, and Naruto's presence could start to change the power dynamics in Esdeath's territory.
One possibility is that Naruto joins Akatsuki to change it from within. He might think he can stop their more evil plans while also learning more about his own powers and the secrets of the ninja world that Akatsuki seems to be involved in.
Well, if Naruto joins Akatsuki in fanfiction, perhaps it's because he's disillusioned with the Hidden Leaf Village for some reason. Maybe he feels betrayed by them. In Akatsuki, he could form unexpected alliances. For example, he might bond with Hidan over their shared brashness in a way, and together they could influence the direction of Akatsuki's actions.
Maybe Naruto joins the Akatsuki with the intention of spying on them for Konoha. He could pretend to be on their side while secretly sending information back to his village. This would add a lot of tension and secrecy to the story as he has to constantly be careful not to be discovered.
Well, it could be about Naruto finding a new group to belong to. Maybe he's lost in a strange world and the horde takes him in. He might bring his ninja skills and unique values to the horde, causing all kinds of changes in their way of life.
In this fanfiction, Naruto could bring his sense of justice to the mafia. He may try to reform it from the inside, facing a lot of resistance from the traditional mafia members who are used to their old ways. His shadow clone jutsu could be used for things like gathering intelligence or creating diversions during mafia operations.
One possibility could be that Naruto goes to Suna to help them with a new threat. Maybe there's a powerful enemy that only Naruto's skills, like his Rasengan and shadow clone jutsu, can deal with. He then starts training some of the Suna ninjas in new techniques, leading to stronger bonds between Konoha and Suna.