Goku's understanding of different universes and races could be deepened in fanfiction. Since Dragon Ball Super introduced the multiverse concept, fanfiction could explore how Goku interacts with and learns from beings from other universes, making him more worldly and less naive in some ways.
One of the interesting power - ups could be his Ultra Instinct form. In fanfiction, it might be further enhanced, like having different levels that are not shown in the original. For example, he could have an Ultra Instinct - Kaioken combination which would be extremely powerful.
In this fanfiction scenario, it could be an extremely emotional encounter. Goku, who has grown so much in Dragon Ball Super, finally meeting his father Bardock. Maybe Bardock gets to see how his son has not only become a powerful Saiyan but also a protector of Earth. It could lead to some interesting exchanges about Saiyan heritage and the future of the Saiyan race.
Caulifla and Goku's relationship in fanfiction could be really interesting. Maybe in this fanfiction, they start as rivals. Caulifla, with her Saiyan pride, wants to prove she's stronger than Goku. But as they fight more, they begin to understand each other's fighting styles and develop a mutual respect. This could lead to some really cool training sessions where they both learn new techniques from one another.
One possible fanfiction idea could be that Goku's daughter has unique powers that are a combination of his Saiyan strength and something new, like the ability to control time on a small scale. She might struggle to fit in with the other Z - fighters at first because they see her as just Goku's daughter, but she proves herself by facing a new, powerful enemy that the others can't defeat easily.
In a fanfiction, Goku might be weakened due to a curse. He loses his Super Saiyan powers and has to start from scratch. This could lead to a great character - development arc. He might discover new ways to fight without relying on brute strength, like using his wits and strategic thinking more, and also learning new martial arts techniques from his human friends.
Perhaps a fanfiction where Vados senses a new threat approaching the universe. She enlists Goku to help her find a way to stop it. Along the way, they encounter strange new races and powers. Goku's simple but powerful approach to fighting combined with Vados' wisdom would make for an interesting dynamic as they search for a solution to this impending doom.
Love and family are common themes. Since Goku and Chichi are husband and wife, many fanfictions explore how they balance their family life with Goku's constant need to fight and protect the universe. It shows how their love endures through all the challenges.
Well, there are some great ones. A lot of fanfiction in this area explores the power of Goku in his SSJ4 form in the context of the Dragon Ball Super universe. Some stories might focus on battles that Goku could have in this form against new and powerful enemies, while others could be about his relationships with other characters while being in this super - powerful state. It really depends on what you're interested in.