Well, in a fanfiction, Bardock might meet Goku when Goku is training. Bardock could offer some unique Saiyan training techniques that Goku has never seen before. This would enhance Goku's power even more. Also, they could have a conversation about their Saiyan heritage. Bardock could tell Goku more about their home planet, Vegeta, and the Saiyan culture that Goku has been mostly cut off from due to being sent to Earth as a baby.
Perhaps Bardock meets Goku in a dream - like realm. Goku, not fully understanding who this strange Saiyan is at first, starts to learn about his father through their interactions. Bardock could then pass on some of his latent Saiyan power to Goku in this spiritual meeting. This would give Goku an unexpected boost in power, which he could later use to defend against new threats in the Dragon Ball Z world.
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.
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.
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.
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.
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 possible change is his power level. Fanfictions often give Goku new power - ups that are even more extreme than in the official story. For example, he could gain a 'Ultra - Ultra Saiyan' form that is many times stronger than the regular Super Saiyan forms. His appearance in this form could be very different, with longer hair, more defined muscles, and a new color to his aura. Another change could be in his family life. Maybe he spends more time with his family, teaching his sons and daughter new fighting techniques that he created himself. This would show a more domestic side of Goku that we don't see as much in the original series.
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.
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.
It could change it a great deal. Goku might learn more about his Saiyan roots earlier, which could potentially make him more in tune with his Saiyan side. This could lead to him training differently or having different goals. For example, he might be more interested in exploring his Saiyan heritage and what it means for his power - up potential.
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.
A popular version of Bardock in fanfiction is the one who has a premonition of the destruction of the Saiyans much earlier. This Bardock then tries to take actions to prevent it, like gathering other Saiyans who might be sympathetic to his cause. It makes him a hero figure right from the start, rather than just a victim of Frieza's wrath as in the original story.