Goku might run into past versions of his friends. He could see a younger Krillin or Bulma and have some really interesting interactions. He could also meet past versions of his enemies and try to change their fates. For instance, he could meet a young Vegeta and try to steer him away from the path of evil. This would be a huge change in the Saiyan's story.
One possible scenario in this fanfiction could be that Android 18 and Goku are forced to time travel due to a new threat that endangers the entire universe. They might travel to a time when the Saiyans first arrived on Earth. Goku, with his knowledge of the future, could try to change some events to prevent future disasters. Android 18, with her strength and unique abilities, would be a great ally in this adventure. They might face challenges like dealing with the primitive technology of that time and also having to hide their true identities to avoid disrupting the timeline too much.
Yamcha could be a good addition. He has his own martial arts skills and a history with Goku. His insecurities about being overshadowed by Goku can be explored in a male - centric fanfiction. Tien is another strong character. His multi - armed fighting style and his disciplined approach to martial arts can make for some exciting scenes when paired with Goku. And let's not forget Gohan. As Goku's son, he has his own story arc and powers that can be incorporated into the fanfiction in an interesting way.
Goku's godlike power might make his time travel more precise. Normal time travel in the Dragon Ball universe can be a bit haphazard, but with his godly energy, he could target specific moments more accurately. For instance, he could arrive at the exact second he wants to in the past or future.
If Goku travels back in time, his relationship with Bulma could be very different. In the past, she was more of a guide to him. But if he goes back with his current knowledge and power, he could become more of a protector for her. He might also be able to prevent some of the dangerous situations she got into in the original story.
Well, his relationship with Vegeta would be interesting. If Goku went back in time and showed Vegeta the SSJ God form too early, Vegeta might become more competitive or even jealous earlier. He might push himself even harder to catch up, which could lead to more intense rivalries and also more joint training sessions between them.
If Goku time travels, his powers could change in several ways. For example, if he travels to a time when the power levels were generally lower, like the early days of the Saiyans, his current power might seem overwhelming. He could easily defeat foes that were once considered strong. However, if he travels to a future where new threats have emerged, his powers might be relatively weaker compared to the local powerhouses. He would then have to train harder and adapt to the new power scale.
One popular theme could be Goku's training adventures from a male character's perspective. For example, a fanfiction might focus on a new male character who joins Goku in his training on King Kai's planet. This allows for exploring new power - up scenarios and the intense training regime that Goku is known for. Another theme could be male friendship. Since Goku is a very friendly and open - hearted character, a fanfiction could delve into his relationships with other male characters in a more in - depth way, like his bond with Vegeta or Krillin. It could show how they support each other through tough battles and share their Saiyan or martial arts knowledge.
His relationship with Vegeta would also change. If Goku goes back to a time when they first met, he could try to befriend Vegeta right away instead of being enemies first. This would change the entire dynamic of their rivalry. They might become allies much sooner and train together, which would lead to both of them becoming even stronger at an earlier stage.
One possible fanfiction could be Gt Goku traveling back in time to prevent the destruction of Earth in an earlier timeline. He could use his knowledge from the GT era to stop a powerful enemy that was previously victorious.