It could be a new Saiyan from another part of the universe who is jealous of the power the family holds. He might come to Earth to challenge the son and prove his own superiority.
Perhaps Gohan's own overconfidence could lead to his death. He might underestimate an enemy's power or a dangerous situation and make a wrong move that results in his end. For example, he could rush into a fight without proper preparation thinking he can handle it easily.
Gohan himself could be a main character in some form. Maybe he exists in Naruto's memories or as a spirit guide. Another potential main character could be Sakura. She might be interested in Naruto's new powers and try to help him understand and control them. And of course, there could be new characters introduced from Gohan's world that interact with the Naruto characters.
Probably Natsu. They both have a strong sense of justice and are very powerful fighters. Natsu's fire - based attacks and Gohan's ki blasts could make for some amazing combined attacks in battle.
Well, it could be about their son inheriting unique powers. Maybe he has a mix of Gohan's Saiyan abilities and Videl's human tenacity. He might start training at a very young age, much like Gohan did, and face challenges that test his limits both physically and mentally.
Naruto would likely have a very different life. He'd grow up in a world full of Saiyans and other Dragon Ball characters. Instead of learning ninjutsu, he might be trained in martial arts and ki control. His friends would probably be different too, like Goten and Trunks. And his goals might shift from becoming Hokage to perhaps protecting the Earth from otherworldly threats like in the Dragon Ball series.
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.
Captain America could be a great ally. His sense of justice and leadership would mesh well with Gohan's own values. They could both lead a team into battle and inspire others with their courage.
Piccolo might also be a savior. He has a soft spot for Gohan since they trained together. He could use his strategic mind and powerful attacks to outwit Raditz and rescue Gohan. Maybe he teams up with Goku for an even more epic rescue mission.
Her relationships with other characters would shape her differently. With Piccolo, he could act as more of a protective figure. Gohan, in turn, would learn different values from him. Maybe she would be more attuned to nature and use it to her advantage in battles, like Piccolo does, rather than just relying on brute strength.