Well, in this kind of fanfiction, it might happen through some sort of cross - dimensional magic. Maybe there's a rift between the Naruto universe and the Dragon Ball universe that allows Naruto to gain the power of a Super Saiyan God. It could also be the result of a powerful wish made by a god - like character who decides to give Naruto this new form for the sake of saving his own universe or something like that.
One reason this type of fanfiction is so appealing is the potential for epic battles. Percy, with his sword and water - based powers, combined with the Super Saiyan God's energy attacks, could face off against some truly formidable foes. And not just in terms of physical combat, but also in strategic battles where he has to use both sets of powers cleverly. Also, the cultural clash between the two worlds can add a lot of humor and interesting plot points.
The main character is Naruto for sure. But in this fanfiction, we might also see characters like Beerus, the God of Destruction from Dragon Ball. Beerus could be interested in Naruto's new - found power and either try to test it or be a threat to Naruto's world. Another important character could be Hinata. She would be concerned about Naruto's transformation and how it affects their relationship. Also, characters like Piccolo could be involved, perhaps helping Naruto understand the ki aspect of the Super Saiyan God power.
In the fanfiction, perhaps there is a prophecy that Naruto will become a Super Saiyan God - like being. As he gradually transforms, his body and mind change. He starts to see the world in a different way. His new powers attract the attention of both friends and foes. His friends try to help him adjust, while his foes try to either steal his power or destroy him. The plot could revolve around Naruto's journey to master his new form, protect his loved ones, and save the ninja world from destruction that only he, with his new powers, can prevent.
In this fanfic, the author could explore the origin of Broly's transformation into a Super Saiyan God. It might be a unique journey, different from how Goku and Vegeta achieved it. Perhaps there's a special training regimen or a hidden power within Broly that was awakened. The story could also delve into how the other characters in the Dragon Ball universe react to Broly's new form. Do they fear him? Admire him? And how does this change the power dynamics in the overall story? There could be epic battles against new foes that only Broly in his Super Saiyan God form can handle.
There's a fanfic where Bardock becomes a Super Saiyan God in an alternate universe. Here, he uses this power to try and change the fate of the Saiyans. The story could show how his newfound power affects his relationships with other characters like Vegeta and Goku, and how he might use it to stand up against the likes of Frieza in a different way than in the original story.