The exploration of new worlds is also common. As Sonic is from his own game - based world and Goku from the Dragon Ball universe, fanfiction writers often create new settings where both characters can interact. This could be a merged universe or a new dimension that they are transported to. These new worlds add an element of mystery and adventure to the stories.
In my opinion, Goku has more experience in fighting powerful opponents on a universal scale. He has fought against gods and demons. Sonic, on the other hand, mainly deals with threats to his own world. But Sonic's speed is not to be underestimated. He could potentially outmaneuver Goku and find a weakness. However, Goku can constantly increase his power during a fight. So, again, it's not clear who would win.
One interesting idea could be the clash of their different power systems. Goku has his ki-based attacks and Super Saiyan forms, while Sonic has his speed and Chaos Emerald powers. Maybe they could have a friendly sparring match to test each other's abilities.
Sure. One popular 'sonic meets goku fanfiction' might be 'Sonic and Goku's Adventure'. In this story, Sonic's speed and Goku's power combine in an unexpected way to face a new, powerful enemy. It has exciting fight scenes and interesting character interactions.
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.
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.
There could also be other characters from the Dragon Ball universe making an appearance. For example, Vegeta might show up. He could be curious about Fem Goku and how she compares to Goku in terms of power. Or Bulma could be there, perhaps she's interested in the technology or biology behind Fem Goku's existence.