One plot idea could be that Baby takes over Goku's body and tries to use his power to conquer the universe in a more subtle way. He might pretend to be Goku at first and manipulate his friends into doing his bidding without realizing it.
One idea could be that Baby Goku discovers a hidden power within himself while on an adventure with Gine. Maybe they encounter a new and strange enemy that forces Gine to teach Goku some unique skills passed down in their family.
One plot idea could be that Bardock, in some way, gets to see the future Goku achieves. Maybe through a time - warp or a prophetic vision. Another could be a story where Baby Goku is sent on a special mission, and Bardock's spirit somehow guides him. For example, when facing a really tough enemy, Baby Goku hears Bardock's voice in his head giving him advice on how to fight.
Well, a great plot could be that in his baby state, Goku attracts the attention of an old enemy who wants to take advantage of his weakened state. His friends then have to protect him at all costs. Also, there could be a plot where baby Goku discovers new powers that are unique to his baby form, like the ability to communicate with animals in a special way.
One idea could be that Goku and Goku Black are forced to team up against an even greater threat from another universe. They start to understand each other's fighting styles during the battle and gradually develop a grudging respect for one another.
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 idea could be a story where Bulma creates a new device that accidentally sends Goku and her to a parallel universe. There, they have to work together to find a way back home while facing new and strange enemies. Another could be a time - travel plot where they go back in time to before Goku met Chi - Chi and Bulma realizes she has feelings for him. The third idea is a story where Goku and Bulma get trapped on a deserted planet and must rely on each other's skills to survive and escape.
One idea could be a crossover universe where Goku somehow ends up in the Naruto world and meets Sakura. They could team up to fight a new common enemy that is causing chaos in both their worlds. Maybe this enemy has the ability to steal energy like the Saiyans but also uses genjutsu like the ninjas.
Maybe there could be a story where Android 18 gets sent to a different dimension and Goku and Vegeta have to follow her to bring her back. In this dimension, the rules of power and fighting are different. They all have to adapt quickly. Goku and Vegeta might learn some new skills from Android 18 as she has a different way of approaching combat situations due to her android nature.
One idea could be Goku ending up in the DC universe and having a friendly spar with Superman. Their different power sources and fighting styles would make for an exciting encounter. Maybe Goku learns about Kryptonite and how it affects Superman, which gives him a new perspective on weaknesses.
One idea could be that Goku discovers Launch's secret love for lemon-flavored treats during a training break. They bond over sharing some lemon candies and it leads to a friendly competition to see who can endure the most sour lemonade. This simple shared interest could strengthen their friendship in the fanfiction.