Shallot can be developed by giving him a backstory. For example, explain where he came from and what his early life was like. This could shape his personality and motives in the fanfiction.
Let him face difficult challenges that force him to grow. Like dealing with a powerful enemy that he can't defeat at first. Through training and perseverance, he overcomes this enemy and becomes stronger both physically and mentally. This kind of development would make him a more interesting and relatable character in the Dragon Ball Z fanfiction.
Another theme is his relationships. This can include his friendships with other characters from the Dragon Ball Z universe. For example, how he interacts with Goku or Vegeta, and how those relationships develop over time. Some fanfictions also explore possible romantic relationships for Shallot.
Another interesting concept would be Shallot getting lost in a different dimension within the Dragon Ball Z universe. He would have to find his way back while encountering strange new races and powers, and along the way, he might learn some valuable lessons about himself and his abilities. This could lead to him coming back to his own world as a much stronger and wiser fighter.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. They usually have a wide variety of Dragon Ball Z fanfictions, including those featuring Shallot.
You need to be familiar with the Dragon Ball universe as a whole. Incorporate other popular characters like Goku, Vegeta, etc. in a meaningful way. Maybe Shallot has a rivalry with Goku that is different from the ones we've seen before. Also, don't be afraid to add your own unique twists to the power - up systems or the lore of the Dragon Ball world. For instance, you could create a new type of Ki that only Shallot can access.
Her character could be developed by giving her unique fighting styles. For example, she could combine Goku's martial arts with some new techniques she invents. This would show her creativity and independence.
They could go through a period of misunderstanding. Maybe Gohan makes a decision about his future that Chichi doesn't initially understand. Through communication and some trials, they grow closer as they learn more about each other's perspectives.
Gohan could be developed by showing more of his academic side in fanfiction. He's smart, and this could be explored further. For example, he could use his intelligence to create new techniques or solve problems that the Z - fighters face. Videl, on the other hand, could be developed by showing her growth as a martial artist outside of just learning from Gohan. She could travel to different dojos and learn from other masters, which would make her an even more formidable fighter in the fanfiction.
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.
They could also develop their relationship through training. If Vegeta takes a more hands - on approach to training Trunks, not just as a student but as his son, they could bond over the shared experience of pushing their limits. They could learn new techniques together and grow closer as a result.
Goku's understanding of different universes and races could be deepened in fanfiction. Since Dragon Ball Super introduced the multiverse concept, fanfiction could explore how Goku interacts with and learns from beings from other universes, making him more worldly and less naive in some ways.