A plot could involve Goku being transported to a future where all his friends are dead and the world is in ruins. The unknown circumstances that led to this and the feeling of helplessness could make him scared. He then has to figure out how to go back in time and prevent this future from happening, all while being afraid of what he might find out about how this came to be.
Maybe in the fanfiction, there's a prophecy that Goku will be the cause of the destruction of the universe. This prophecy shakes him to his core as he has always been a protector. The thought that he could be the cause of such destruction makes him scared. He then embarks on a journey to try and change his fate, all while being haunted by this fear.
One possible fanfiction could be where Goku is faced with an otherworldly entity that he can't sense or understand. This makes him scared as his usual confidence in his power is shaken. Maybe it's a being from a different dimension that defies all the rules he knows about fighting.
One possible plot could be that Android 21, with her unique powers, teams up with Goku to face a new and powerful enemy. They might have to combine their strength and fighting techniques to defeat this foe.
In the fanfiction plot, Goku might be on a quest to save the universe when he stumbles upon a time - rift. Through this rift, he meets his mother. She has knowledge of an ancient Saiyan prophecy that Goku is a part of. Together, they work to figure out how to fulfill the prophecy and save the universe. Along the way, Goku gets to know his mother better, and she becomes an important figure in his life, guiding him both in battles and in his personal growth.
Well, it could be that Goku meets Bardock in a dream - like state. Bardock appears to Goku to pass on some long - lost Saiyan knowledge or a special technique. Goku, being eager to learn more about his heritage, listens intently. As they interact, Goku might feel a deep connection to his father that he never felt before. This could also lead to Goku having a new understanding of his Saiyan nature and using it to become even stronger in his future battles.
One possible plot twist could be that Kid Goku is actually from an alternate timeline and has some powers that Dragon Ball Z Goku doesn't expect. Another could be that a villain uses their meeting to his advantage, like creating a rift between them to cause chaos.
One possibility is that Gine could train Goku in some long - forgotten Saiyan techniques. Since she is his mother, she might know some unique skills that could make Goku even stronger.
In some fanfictions, Goku and Raditz could form an unlikely alliance if they were faced with an even greater threat. For example, if a new and extremely powerful enemy emerged that threatened not just Earth but the entire Saiyan race. Raditz, who initially came to Earth with the intention of conquering it, might see the need to team up with Goku to save their home planet. Goku, being the good - hearted Saiyan he is, would be open to the idea if it meant protecting his loved ones.
In this kind of fanfiction, Goku might lose his family. For example, his friends and loved ones could be killed by a powerful new enemy. This would leave him in a state of deep despair and loneliness, and he would have to find a way to carry on without them.
He could die in battle. Maybe a new, extremely powerful villain emerges who has the ability to nullify Goku's powers or is just so strong that Goku's attacks have no effect. After a long and intense fight, Goku is defeated and dies.
In this fanfiction scenario, Goku meeting Gine could be really interesting. Gine is Goku's mother, and in a fan - made story, their meeting might involve Gine finally seeing how strong her son has become. Maybe she'd be proud of all his achievements in protecting the Earth and the universe. It could also be a very emotional encounter as Goku has grown up without her presence for most of his life.