One way to develop their characters is to put them in situations that force them to grow. For example, if they were stranded on a hostile planet. Bardock would have to rely on his wits and not just his strength. Fasha could show her nurturing side, taking care of Bardock when he's injured. This would show different aspects of their personalities and help in their character development.
One idea could be exploring their relationship before Bardock was sent on his final mission. Maybe a story about them training together and sharing their dreams for the future 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 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.
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.
There might be a fanfiction that focuses on Fasha's relationships. For example, it could explore her friendship with Bardock in more depth, showing how they supported each other during their Saiyan days. This could include flashbacks of their training together and the challenges they faced as young Saiyans.
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.
Goku is a great character to pair with Bardock. Since Goku is his son, it can create some really emotional and action - packed scenes. They can train together or fight side by side against common enemies. Another good option is Vegeta. Their different personalities as Saiyans can lead to interesting interactions. Bardock's old - school Saiyan ways compared to Vegeta's pride can make for some engaging storylines.
One interesting 'Dragon Ball Z Bardock' fanfiction could be about Bardock surviving and coming back to change the course of Saiyan history. It might explore his relationships with other Saiyans in a new light, like how he'd interact with Goku differently.
There are some fanfics that focus on Bardock's pre - destruction memories and how they might influence his actions if he were to come back. For example, a story could explore how his love for his family and his hatred for Frieza's tyranny would drive him to train Goku in a different way. He might pass on some of the ancient Saiyan techniques that were lost over time. This could lead to Goku achieving new forms or powers much earlier in the story, which would have a huge impact on the battles against the likes of the Saiyans, Frieza, and the Androids.