One of the characters who could betray Goku is Piccolo. Although they've been allies for a long time, in fanfiction, things can change. Perhaps an ancient evil force takes control of Piccolo's mind and makes him turn on Goku. Or it could be Krillin. He might be influenced by an outside force that convinces him Goku is becoming too dangerous. Also, don't forget about the Kais. If there's some sort of power imbalance or a threat they perceive from Goku, they might betray him to maintain the order of the universe in the fanfiction.
In 'Goku betrayed fanfiction', a common plot might be the corruption of his power. Let's say Goku discovers a new form of power that is seen as too dangerous by others. His friends and even some of the Z - fighters fear that he'll lose control and turn on them. So they decide to betray him first to protect the Earth. Another aspect could be a political betrayal. If there were some sort of intergalactic politics involved, Goku might be sacrificed or betrayed by his own side to make a deal with a more powerful alien race. And then there's the idea of a time - travel - related betrayal. Maybe someone from the future comes back and convinces everyone that Goku will cause a great disaster in the future, causing them to betray him in the present.
Perhaps in the fanfiction, an evil version of Goku from an alternate timeline arrives. This impostor causes chaos and destruction, but everyone blames the real Goku. His family and friends are deceived by the look - alike. Goku tries to prove his innocence but no one will listen. He might have to find a way to expose the impostor and regain the trust of those he loves.
In the 'goku and gohan betrayed fanfiction', perhaps they are betrayed due to a misunderstanding. Say, Goku makes a deal with an unknown force to save the universe, but it's misconstrued as him allying with the enemy. Gohan, being associated with Goku, is also seen as a traitor. And this misunderstanding could be spread by a character with their own motives, like a power - hungry individual who wants to take over the Z - fighters' leadership.
It could be Vegeta. Maybe in this fanfiction, his pride gets the better of him and he feels overshadowed by Goku and Gohan's power. So he fabricates some lies to make them look like traitors to the rest of the group.
Maybe it's a new character created specifically for the fanfiction. This character could be a powerful sorcerer who has the ability to manipulate people's minds. He targets Goku out of jealousy for his power and popularity. By using his mind - control powers, he makes everyone around Goku believe that he's a traitor, thus making himself the main antagonist.
One common plotline could be Goku being betrayed by a former ally who is jealous of his power. For example, a fellow Z - fighter might feel overshadowed and make a deal with an enemy to take Goku down. Another plotline could involve Goku being betrayed by someone he trusts from his home planet, who has been corrupted by an evil force. It could also be that a new character, who initially seems friendly, betrays Goku in order to steal his Saiyan powers for their own dark purposes.
Well, Vegeta would be a likely character. He might be initially suspicious of the female Goku. Maybe he thinks she's a threat or just can't believe there's another Goku - like being. He could be there to add some comical moments as he tries to understand the situation.
Another possible main character could be the villain that forces the two Gokus to meet. This villain could be a new, super - powerful threat that the two Gokus need to deal with. Their meeting becomes a crucial part of the story to defeat this powerful foe.
Well, it could be about Goku Jr learning some of Goku's most powerful moves. Maybe Goku teaches him the Kamehameha. They might also go on an adventure together, like fighting a new and powerful enemy that neither could face alone.