One idea could be to focus on Bardock's perspective before his fateful battle. Maybe explore his thoughts about his son Goku being sent to Earth and his own impending doom. He could have some premonitions about Goku's future role in saving the universe.
Another potential rival could be a young, prodigious martial artist from a new school of martial arts on Earth. This character could be jealous of Goku Jr's fame and constantly try to outdo him in battles and in the eyes of the public. He might use unorthodox techniques that Goku Jr has to quickly figure out how to counter.
Well, in this fanfic, things might change in terms of character development. Maybe Piccolo becomes more powerful or Konna undergoes a significant transformation. Also, the story's setting or the relationships between characters could undergo alterations.
Well, it could be about Goku Jr learning some of Goku's most powerful moves. Maybe Goku teaches him the Kamehameha. They might also go on an adventure together, like fighting a new and powerful enemy that neither could face alone.
To develop Goku Jr's character further, he could be given more complex emotions. For example, showing his fear in the face of truly overwhelming enemies, rather than always being fearless like Goku. This would make him more relatable. Also, exploring his relationships in more depth, like his friendship with Pan. Maybe they have a falling out over different views on how to protect their world, which forces Goku Jr. to grow and understand different perspectives.
Maybe an old enemy of Goku's who has somehow managed to return. This enemy has heard about Goku Jr and figures that by attacking him, he can get revenge on Goku. This could be someone like Frieza who has found a new way to be resurrected and is more powerful than ever.
One great DBZ Goku Black fanfiction is 'The Blackened Saiyan'. It explores an alternate universe where Goku Black's reign of terror takes some unexpected turns. The story delves deep into his character, showing his motives and how the other Z - fighters react to his presence. It has some really intense battle scenes that are well - written.
In fanfiction, the unique aspect of Goku and 18 is their contrasting natures. Goku is a Saiyan, full of energy, always eager for a fight, and has a somewhat innocent view of the world. 18, on the other hand, is an android, created with a more cynical view due to her origin. Their interactions can be really interesting as they bridge these two different outlooks. For example, Goku's positive attitude might start to change 18's more negative perspective over time.