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 scenario could be an emotional reunion. Bardock, having seen Goku's future through his premonition ability, might be filled with pride. He could see how Goku has grown and the hero he has become in protecting the Earth. Another scenario could be Bardock arriving at a crucial moment during a battle Goku is in and lending his Saiyan strength to help Goku out. This would not only show their Saiyan connection but also the power of family unity in the Dragon Ball Z universe.
A fanfiction might explore the idea of Bardock seeing Goku's life through a time - space rift. He witnesses all of Goku's battles and the friends he makes. Bardock is filled with pride but also realizes that Goku has a different path than the traditional Saiyan way. This makes him question the Saiyan culture he once knew. Meanwhile, Goku starts to have strange dreams about his father, which leads him to search for more about his Saiyan heritage.
One possible plot for this fanfiction could be that Bardock's return is not a simple one. He might be brought back by some sort of time - travel or resurrection magic. His return could stir up old rivalries among the Saiyans. And as he tries to fit into the current Dragon Ball Z universe, he discovers a conspiracy that threatens not only the Saiyans but the entire universe. So, he has to fight against this conspiracy while also trying to reconnect with his son Goku in a more meaningful way.
One possible plot could be that Goku, having achieved new levels of power, somehow travels back in time to meet Bardock. Bardock, initially shocked, quickly realizes this is his son. They could have a sparring session where Bardock sees the full extent of Goku's power and is proud. Then they might sit and talk about Goku's life on Earth, and Bardock could share some of his own past battles and the reasons he sent Goku away.
Bardock is a tough and battle - hardened Saiyan. When he meets Goku, who has a more pure - hearted and friendly personality, there could be an interesting contrast. Bardock might be initially skeptical of Goku's 'soft' ways but then come to respect his strength which comes from his good heart. Goku, on the other hand, would be curious about his father and would try to show Bardock the value of protecting others, not just for the sake of battle like the Saiyans usually do.
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.
A possible plotline could be that Bardock, in the afterlife, is able to communicate with Goku in his dreams. He warns Goku about an upcoming threat that is even more powerful than the villains he has faced so far. Goku then starts a new training regime in preparation for this threat, and along the way, he discovers more about his father's past and the true potential of the Saiyan race.
One great Bardock in Dragon Ball Z fanfiction is often depicted as a fearless and noble Saiyan. He is shown as a warrior who, despite the cruel nature of the Saiyan race at that time, had a sense of honor. In some fanfictions, he manages to break free from the control of Frieza in more creative ways than in the original story, making his character even more complex and interesting.
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.
Well, it could vary a lot. In some fanfics, Bardock might be reborn with new powers or a different destiny. Maybe he gets to change the future of the Saiyan race. But it really depends on the author's creativity.