One possible plot could be Goku and Turles forced to team up against a new, powerful enemy. Maybe a villain from another dimension that threatens both their home planets. This would force them to put aside their differences and combine their unique fighting styles.
Their relationship could develop through mutual respect for each other's strength. Goku, being the pure - hearted Saiyan he is, might start to see that Turles has potential for good deep down. Turles, on the other hand, could be in awe of Goku's power and gradually change his view of Goku from an enemy to a rival and perhaps even a friend.
Well, obviously Turles and Goku are the main characters. Turles is often depicted as the villain in the original story, but in fanfiction, he can be portrayed in different lights. Goku, on the other hand, is the hero. Their interactions and the development of their relationship form the core of the fanfiction.
One idea could be a story where Goku and Turles are forced to team up against a new, even greater threat to the universe. They start off distrusting each other due to their past but gradually learn to work together and respect one another's strength.
First, think about the basic plot. Decide if it's going to be an adventure, a character - study, or something else. For example, if it's an adventure, figure out what kind of adventure they'll go on.
Perhaps in a different universe, Turles and Goku are brothers. They grow up together, training side by side, but then a prophecy divides them as they are told one must defeat the other for the greater good. This creates a complex relationship full of love, rivalry, and moral dilemmas.
Maybe a fanfic where Goku discovers Turles has a different side to him. Turles could be in a situation where he has to protect something or someone innocent, which makes Goku see him in a new light. They then have to work together to keep this innocent thing safe from other villains in the Dragon Ball universe.
One common theme is rivalry - turned - friendship. Their initial intense rivalry gradually transforms into a deep bond as they face various threats. Another theme is power - up. They often find new ways to increase their power together, like in some fanfictions where they discover a new fusion technique.
The relationship could start with hostility. Towa might see Goku as a threat to her plans and Goku sees her as an evil force. But then, when they are forced into a situation where they need to rely on each other, like being stranded in a strange realm. They begin to see each other's strengths. For example, Goku might admire Towa's intelligence in dealing with the strange environment, and Towa might be impressed by Goku's unwavering determination.