It could be a genetic mutation in the fanfic's storyline. Some strange event or factor could have caused a change in Bardock's genes, making it possible for him to become Super Saiyan. This genetic change might be related to some ancient Saiyan lore or a new element introduced in the fanfic's universe.
Well, if Naruto goes Super Saiyan 3 in a fanfiction, he would likely gain an insane amount of power. His physical abilities would skyrocket. He could move at incredible speeds, and his strength might be enough to shatter mountains. His chakra would probably combine with the Saiyan power in some unique way, creating new and powerful jutsu.
Well, in this fanfiction concept, Naruto going Super Saiyan 4 could also lead to some interesting character dynamics. His friends might be initially shocked and a bit scared of this new form. Naruto would then have to prove that he's still the same person despite this radical transformation. And as for the enemies, they would surely be caught off - guard and have to quickly come up with new strategies to deal with this super - powered Naruto.
Obviously, Goku would be a main character he'd interact with. If he goes back to when Goku was a kid, he could train with him, or try to convince Goku's grandpa to let him train Goku in a different way. Another character would be Bulma. If he goes back far enough, he could meet a younger Bulma and perhaps change their relationship dynamics. He might also interact with his younger self. This could lead to some really interesting self - reflection and growth as he tries to guide his younger, more hot - headed self.
Another plot could be that a mysterious entity bestows the power of Super Saiyan Blue on Naruto. He then has to keep it a secret from his friends and village while also using it to protect them from a new and powerful enemy. This would create a lot of internal conflict for Naruto as he tries to balance secrecy and heroism.
One great Super Saiyan Blue Goku crossover fanfiction is 'Goku in the DC Universe'. It's really exciting to see Goku interact with Superman and other DC heroes. He has to adjust to the different power levels and rules in that universe.
Sure does. Goku attains the perfected SSJB in the manga during intense battles and as part of his power-up journey. It's a significant moment for his character development.