In a fanfiction where Future Gohan meets Goku, it could be an emotional reunion. Gohan might be filled with a sense of relief and joy, seeing his father again. He could show Goku all the things he's been through in the future, and Goku would be both proud and sad about what his son has endured.
One possible scenario in this fanfiction could be that Future Gohan brings a warning from the future. He could tell Goku about new threats that are emerging in his timeline. Goku, being the hero he is, would then start to plan and train to face these potential threats, perhaps even enlisting the help of his friends. And Gohan would stay by his side, just like old times, ready to fight alongside his father.
In the fanfiction, perhaps they team up to fight a common enemy. Goku's raw power combined with Gohan's strategic mind from the future battles could make them an unbeatable duo. They'd exchange blows and strategies, and their teamwork would be amazing to read about.
In such a fanfiction, perhaps future Gohan could warn present - day Gohan about upcoming threats that he has faced in his own timeline. He might share his experiences and knowledge, which could make present Gohan a stronger fighter and a wiser person.
One possible interaction is that Bardock could spar with Goku and Gohan. He'd test their limits and see how much they've learned about fighting. Another could be Bardock sharing stories of Planet Vegeta with them, which would be really interesting for Goku and Gohan to hear.
A possible plot twist could be that future Gohan is actually an impostor sent by an enemy to manipulate the real Gohan. Another twist might be that when they meet, their powers combine in an unexpected way that causes some sort of time rift or a change in the timeline.
Goku and Grandpa Gohan's interaction could be full of wisdom - sharing. Grandpa Gohan was a wise man, and he would pass on more of his knowledge to Goku. Goku, in turn, would tell Grandpa Gohan about all the new friends he has made and the different planets he has visited. They might also spar a bit, just like in the old days, with Grandpa Gohan giving Goku some pointers.
One possible plot could be Goku reminiscing about his past with Grandpa Gohan. Maybe he visits the place where they used to train together. He could find an old relic or something that Grandpa Gohan left for him, which triggers a flood of memories and emotions. This would be a heartwarming story about their relationship.
In this fanfiction, Bardock might be shocked to see how much Goku has grown and the family he has built. He could be proud of Goku for becoming such a strong and kind - hearted Saiyan. And when he meets Gohan, he might see the potential in him as well, maybe even offer some unique Saiyan training tips that are different from what Goku has taught Gohan.
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.
In a fanfiction, Future Gohan could potentially defeat Black Goku. Gohan has shown great power in the past, and if he were to tap into his hidden potential again, he might be able to overpower Black Goku. However, Black Goku is also extremely strong, so it would be a very tough fight.
The plot could also focus on their relationship. Since they are brothers but from different timelines in a way. They could bond over family stories that Goten has heard but Gohan can now give a different perspective on, like stories about their father. And they might train together to become even stronger for the future battles that Gohan foresees.