It could be Vegeta. Maybe Vegeta does something really underhanded like stealing Goku's senzu beans or trying to take all the credit for a victory that Goku also contributed to. Goku, being a fair - minded person, would get angry at such behavior.
Often, Kid Goku is portrayed as the carefree and adventurous type. He's always looking for the next exciting thing to do, whether it's chasing after a strange animal or exploring a new area. He might be a bit naive in some aspects, especially when it comes to things like emotions.
There could also be a moment of self - discovery for both of them. Goku might see his past self in Kid Goku and realize how far he has come, while Kid Goku could get a glimpse of his future potential through meeting his adult self. They could share stories about their friends and enemies, like how Goku could talk about Vegeta and Frieza to Kid Goku, and Kid Goku could tell Goku about his early battles with the Red Ribbon Army.
It's hard to say. Adult Goku has more experience and has achieved higher power levels. But Kid Goku has an unbridled potential that could make him a formidable opponent even to his adult self.
One popular storyline could be their adventures together in the mountains. They might encounter strange creatures and have to use their wits and skills to overcome difficulties. For example, they could find a lost magical item and have to return it to its rightful place.
In the fanfiction, their relationship could be one of mutual admiration. Kid Goku would look up to Future Goku for his experience and power. Future Goku, on the other hand, would be charmed by Kid Goku's innocence and raw potential. They could train together, and during this process, they would form a strong brother - like relationship.
In a fanfiction where Kid Goku meets Future Goku, one possibility is that Future Goku would be amazed at seeing his younger self. He might share some of the dark experiences he has had in the future, like the battles against powerful enemies and the losses. Kid Goku, being young and full of energy, could be inspired by Future Goku's strength and determination. Maybe he would start training even harder, eager to reach the level of his future self.
Well, perhaps in the fanfiction, Goku gets mad when he discovers that someone has been using his name for evil deeds. This would go against his values of justice and protecting the innocent. He might get really angry and go on a search to clear his name and stop the impostor. Or it could be that a new, extremely powerful villain emerges and starts to destroy planets without any remorse. Goku, being the defender of the universe, would be enraged by such senseless destruction and would confront the villain with all his might.
One reason could be ChiChi's overbearing nature. She is often very strict about Goku's training and how he spends his time. In fanfiction, this could be exaggerated to the point where Goku finally gets fed up. For example, if she constantly nags him about not doing enough chores around the house instead of training, it might push Goku to his limit.
It could be about a good kid in a mad or chaotic city. Maybe it's a story of how the kid copes with the craziness around, like dealing with crime, strange people, or just the fast - paced and unpredictable nature of the city.