The main characters are Goku, a Saiyan who is the hero of the story. Vegeta, another Saiyan who starts as an enemy but later becomes an ally. Gohan, Goku's son. Piccolo, a Namekian. Krillin, Goku's best friend. And Bulma, who is important for inventing things that help the characters in their battles.
Vegeta could also work well. Vegeta's pride and determination, along with his powerful fighting skills, would contrast nicely with the Supreme Kai's more reserved and wise nature. They could learn from each other and have some intense rivalries within the story.
The story of Dragon Ball Z Kai follows Goku and his friends as they defend the Earth from various powerful threats. It includes battles against villains like Frieza, Cell, and Majin Buu. Goku, a Saiyan, constantly trains to become stronger and uses his martial arts skills and special abilities like the Kamehameha wave.
One interesting Dragon Ball Z Kai fan fic could be one that focuses on an alternate timeline where Goku never hit his head as a baby. This would change his personality and the entire course of the story. Another could be a story centered around Vegeta's training in a new, uncharted planet, exploring his growth without the constant presence of Goku. There are also fan fics that might explore the backstories of minor characters like Yamcha or Krillin in more depth, which can be really fascinating.
Trunks could be another character. Given his experience with time - travel in the original story, he would have a natural connection with the Supreme Kai of Time. He could be involved in helping her to fix any disruptions in the timeline that he may have knowledge about or be a part of. His future - savvy perspective could be valuable in the fanfiction's plot, especially when dealing with potential threats to the future that are related to the time - space continuum.
One option could be to search on popular online shopping platforms specifically targeted at Indonesian customers. Another possibility is to check with local libraries that have a collection of manga. You could also ask at comic conventions or events related to anime and manga in Indonesia.
There are fanfictions that focus on their family life. For example, a story might explore how Vegeta adjusts to being a father while still maintaining his Saiyan warrior pride. He might struggle with balancing training and spending time with his family, but Bulma is always there to keep him in check.
Goku is, without a doubt, one of the most popular. His constant pursuit of strength and his ability to overcome seemingly impossible odds make him a favorite for fanfiction writers. They can create all kinds of new adventures for him, like facing off against cosmic threats even greater than what he's encountered in the shows.
Another theme is family. Since they have a family in the series, fanfictions often focus on how they raise Trunks and Bulla, and the challenges they face as parents. For instance, Vegeta trying to pass on Saiyan values while Bulma wants to give their kids a more normal human upbringing.