In a fanfiction, anything can be possible. Maybe the author creates a crossover universe where the Naruto and Dragon Ball universes collide. It could be due to some magical or scientific experiment that links Naruto and Trunks as brothers. However, this is completely against the original storylines of both Naruto and Dragon Ball, but that's the fun of fanfiction - to explore wild and creative ideas.
A typical plot device could be a power - up related to their brotherhood. Since Naruto has his chakra and Trunks has his Saiyan strength, they might discover a new combined power because they are brothers. Also, there could be a time - travel element involved. Trunks is associated with time travel in Dragon Ball, and this could be used in the fanfiction to explain how Naruto and Trunks' relationship came to be. For instance, Trunks could travel to the Naruto universe and somehow become related to Naruto through some time - warped event.
In this fanfiction plot, Trunks is on a mission to find a powerful energy source and ends up in Naruto's world. He meets Naruto who is on a mission to retrieve a stolen ninja scroll. They decide to help each other. As they work together, they discover that an evil organization from another dimension is planning to invade both their worlds. Trunks and Naruto then gather their allies from both universes. Trunks brings in Vegeta and Goku, while Naruto gets Sasuke and the other ninja. Together, they form a powerful alliance to fight against this inter - dimensional threat.
In a scenario where Trunks meets Naruto, their meeting would likely be a clash of two very different cultures. Trunks is used to a world where fighting is often about protecting the Earth from powerful alien threats. Naruto is focused on protecting his village and the ninja world. However, they both have a strong sense of justice. So, they might team up to take on a common enemy that threatens both their worlds, using their unique powers and skills to defeat the foe.
First of all, Naruto's sage mode gives him enhanced perception and strength. Trunks could benefit from this by having Naruto share his sage chakra with him. This could potentially give Trunks a new form or boost his existing abilities. On the other hand, Trunks' energy attacks could be channeled through Naruto's chakra pathways. This would allow Naruto to use ki - like attacks without having to learn the ki - manipulation techniques. They could also combine their defensive abilities. Naruto's chakra shields and Trunks' ki - based defenses could merge to create a super - strong shield against powerful attacks.
The relationship between Naruto and Bulma would be really fascinating. Since they are from two very different worlds, seeing how they interact, fall in love, and build a family would be a major plot point. Also, how Naruto would train Trunks in his own ninja - like way while Trunks also has his Saiyan powers would add a lot of depth to the story.
A good crossover idea is that the Akatsuki from Naruto are interested in the technology that Future Trunks has. They might try to steal it for their own purposes. This could lead to a series of battles and alliances. Also, since both Future Trunks and Naruto have a strong sense of justice, they could start a movement in both worlds to promote peace and cooperation between different races and species.
Another possibility is that he could be the brother of Weiss. Weiss comes from a wealthy and proper family. Naruto's more free - spirited and unorthodox ways would clash with Weiss's upbringing at first, but they could grow to understand and support each other as the story progresses.
Yes, there are likely fanfictions out there with such a concept. Fanfiction writers often come up with creative and unexpected crossovers like this. You can search on popular fanfiction websites such as Archive of Our Own or FanFiction.net to find stories based on this idea.
In this kind of fanfiction, it might be that there's a special crossover event. For example, perhaps there's a powerful entity that messes with the fabric of reality and combines elements from the Naruto and Dragon Ball universes in a strange way. This could lead to Naruto being Trunks' dad in this fictional setting. It's all about the creativity of the writer who wants to explore new and unexpected relationships between different fictional worlds.