In a 'naruto son of gohan fanfiction', perhaps Naruto is born with a special power that is a combination of his own ninja abilities and some latent power from being related to Gohan. This could lead to him being an outcast at first in the ninja world as his powers are so different. But as he grows, he learns to master them and use them to protect his village and the world from new threats.
I'm not aware of any such fanfiction. The relationship between Grandpa Gohan and Son Goku in the original story is one of love and mentorship, so this kind of dark and negative portrayal in fanfiction is not common that I know of.
In this fanfiction, Gohan as a girl could bring a new dynamic to her relationships. She might have a different kind of friendship with Videl. Instead of the typical male - female relationship they had before, it could be more of a sisterly bond where they support each other in different ways, like in fighting crime together in a more united front.
This idea is quite out - there in fanfiction. One way it could work is if there are some powerful deities or beings in both universes who decide to manipulate the fates of characters. They could use their powers to transplant Naruto's essence into a new world where Gohan and Videl exist and make them his parents. However, this would completely change Naruto's origin story and his character development would have to be re - imagined in the context of the Dragon Ball world, which has very different power systems and cultures compared to Naruto's world.
One common theme is adventure. Since Gohan has his Beast form, they might go on adventures together fighting enemies. Another theme could be romance, exploring their relationship deeper.