Trunks is another good option. His time - traveling experience and sword - fighting skills could add a new dimension to the crossover. He and Xeno Goku could work together to prevent disasters in different timelines.
One reason is the unique take on Naruto's powers. Ultra Instinto gives a new dimension to his abilities, making battles more exciting. It allows for creative interpretations of his character growth. Also, fanfics in this genre often explore uncharted territories in the Naruto universe, like new relationships or different power hierarchies.
To write a great Naruto Ultra Instinto fanfic, start with a strong plot. Maybe something that revolves around a new threat to the Hidden Leaf Village that only Naruto's Ultra Instinto can counter. Develop his relationships with other characters in the context of this new power. Use vivid descriptions to bring the battles and the world of Naruto to life. And don't forget to proofread for grammar and spelling errors.
Another plot could involve Xeno Goku getting stranded in a different anime world during the crossover. He has to adapt to the new rules and powers there while also trying to find a way back home. He could make new friends and enemies in this strange world.
Yes, it is possible. In fanfiction, writers have the creative freedom to reimagine the origin of characters. Goku being born with Ultra Instinct can add a whole new layer to his character development. It could mean that his power growth would be different from the original story, perhaps faster or with different challenges along the way.
You could write a fanfiction where Goku teaches others about Ultra Instinct. Maybe he tries to pass on this power to Gohan or Trunks. This would involve Goku having to understand the power more deeply himself in order to teach it, and it would also be a great way to develop the other characters.
Goku definitely masters Ultra Instinct in the manga. This transformation gives him a huge boost in power and allows him to take on even stronger opponents.