Goku in the manga doesn't hit a power level of 8000. The power escalation in the story doesn't go that high for him. There are various factors and story arcs that determine his power growth, but 8000 isn't one of them.
Hit would also make for a fascinating pairing. Hit is a skilled assassin with time - manipulation abilities. He could be a great foil to Goku Black. Maybe Goku Black tries to outwit Hit in his time - stop techniques, or they could form a temporary alliance based on their mutual desire to eliminate certain opponents in the tournament. There would be a lot of cat - and - mouse action between them.
Goku's power is measured in different forms and levels in his universe. When it comes to Legendary Pokemon, some of them have the ability to control elements like time and space. In a fanfic, Goku in his Super Saiyan Blue form might be able to match the power of a Legendary Pokemon like Palkia, which has power over space. But it also depends on the situation. If Goku is in an environment where his Ki attacks are less effective, like in a dimension where psychic powers are dominant, he might have a harder time against a Legendary Pokemon like Lugia. Overall, it's a complex comparison as their powers are quite different in nature.
Well, Goku's power level progression could be different in that he might be more in control of it. Since the head injury had some impact on his psyche, without it, he could have a more calculated approach to increasing his power. He might not rely as much on the Kaioken technique, which was developed in part due to his need to overcome limitations caused by his injury - affected development. Instead, he could focus more on pure Saiyan power - up methods like the Great Ape transformation and evolving it further.
One possible storyline could be that Naruto is somehow transported to Goku Black's universe. There, he has to face Goku Black who sees him as an intruder. Naruto would have to quickly learn about Goku Black's powers and find a way to fight back using his ninja skills. Another storyline could be that a powerful villain creates a rift between their two universes and pits them against each other. They start off as enemies but then realize they are being manipulated and team up to fight the real villain.
There could be a storyline where Beerus, out of boredom, decides to train Goku Black instead of fighting him. But Goku Black misinterprets this as a sign of weakness and attacks Beerus. This could lead to a battle where Beerus has to hold back at first to avoid killing Goku Black, but as the fight progresses, he realizes he has to use his full power to subdue him.
Obviously, Goku is one of the main characters. Since it's about him being born with a high power level. And his parents might also be important characters as they would be related to his birth and the discovery of his high power level. Maybe there are also some Saiyan elders or trainers who play a role in his life as they would be interested in his power.
In some fanfictions, Goku Black has been depicted as having a hidden power reserve. In the Tournament of Power, he could tap into this reserve and achieve a new level of transformation. This new form would give him increased speed, strength, and energy projection. He might use this form to take on multiple strong opponents at once, like the powerful warriors from Universe 7 or other universes. His attacks could become more unpredictable, such as his energy beams changing direction mid - flight to catch his foes off - guard.
One interesting fanfiction could be about Goku and Black Goku teaming up against an even greater threat from another universe. In this story, they might initially be at odds but gradually learn to work together, using their unique abilities to save the multiverse.
In fanfiction about Goku and Goku Black, a common concept is the alteration of their power levels. Writers may give Goku new forms or boost Goku Black's abilities in unexpected ways. There can be stories centered around Goku Black's adaptation to the main timeline's culture and society. For example, he might have to deal with the everyday life in addition to his evil plans. And there are fanfictions that focus on the psychological impact of their battles on each other, like how Goku might be affected by constantly facing an evil version of himself.