In some 'Goku meets Goku fanfiction', they could team up against a super powerful enemy that neither could defeat alone. They would combine their signature moves like the Kamehameha for an ultimate attack.
In some versions, the female Goku could be part of a prophecy. The two Gokus meet, and at first, there is some confusion and misunderstanding. But as they get to know each other, they discover that they are key to fulfilling the prophecy. They combine their powers and defeat an ancient evil that was threatening both of their worlds.
One interesting scenario could be when Goku returns from a long and difficult battle. Chichi is overjoyed to see him alive and well. They share a tender kiss filled with all the emotions of relief, love, and longing that had built up during his absence.
In some fanfictions, Goku could snap at Chichi when she tries to interfere with his decision to fight a powerful enemy. Goku is very dedicated to protecting the Earth and if Chichi tries to stop him in a way that he feels is wrong, it could lead to him snapping. For example, she might be worried about his safety but he sees it as her not believing in his strength. This can create a lot of tension between them and lead to an interesting plot development where they have to work through their differences.
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.
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.
Perhaps they would team up against a common enemy. In fanfiction, new threats are often created. They could combine their strength and unique techniques to defeat the bad guy.
In this fanfiction, they might have an epic sparring session. Goku could pass on some of his old fighting techniques to Goku Jr.
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.
One interesting fanfiction could be about Goku and Black Goku teaming up against an even greater threat from another universe. In this story, they might initially be at odds but gradually learn to work together, using their unique abilities to save the multiverse.