A really interesting plot could be set in an alternate universe where Goku and Launch are arranged to be married for some political reason in the Saiyan or Earthling world. They start off not really liking each other but as they face challenges together, they fall in love. For example, they have to deal with a group that is against their union and in the process, they learn about each other's strengths and weaknesses.
Perhaps a time - travel based fanfiction. Goku accidentally travels back in time and meets a younger Launch. He doesn't want to disrupt the timeline but ends up having to work with her to stop a threat that could change the future. This would be a great opportunity to explore their relationship in a different time period and see how their personalities interact in a new context.
One idea could be that Goku discovers Launch's secret love for lemon-flavored treats during a training break. They bond over sharing some lemon candies and it leads to a friendly competition to see who can endure the most sour lemonade. This simple shared interest could strengthen their friendship in the fanfiction.
One idea could be that Goku and Goku Black are forced to team up against an even greater threat from another universe. They start to understand each other's fighting styles during the battle and gradually develop a grudging respect for one another.
Maybe the goddess has a prophecy about Goku being the key to saving her realm from an ancient evil. So she forms a bond with Goku, and as they get to know each other better, Goku starts to develop feelings for her. Their relationship then becomes a driving force for him to fulfill the prophecy and defeat the evil, all while exploring the unique aspects of their two different worlds.
In a fanfiction, there could be a scenario where an ancient prophecy foretells of a combined power of Trunks and Goku being the only thing that can stop an impending doom. They start training together to master a special fusion technique that no one has ever attempted before. Along the way, they face challenges not only in their training but also in dealing with their own egos and differences in fighting styles.
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.
One idea could be that the OC is from a different dimension and has a unique power that Goku Black is intrigued by. He decides to use the OC to further his own evil plans at first, but then starts to develop unexpected feelings. Another plot could be the OC being a time traveler who tries to stop Goku Black's rampage, but gets caught in his web of lies and manipulation. A third option is the OC is a Saiyan hybrid who is initially on Goku Black's side because she is misled by his false charm, and then has to face the truth and make a difficult choice.
One idea could be exploring their relationship in an alternate universe where they succeed in their plans. Another could be a story where Goku Black has a change of heart due to his connection with Zamasu and tries to stop their destructive ways. Maybe a plot where they face a new enemy that forces them to reevaluate their alliance.
One idea could be exploring a time when Sanzo loses his memory and Goku has to help him remember who he is and their mission. This would create a lot of emotional moments as Goku tries to jog Sanzo's memory with their shared experiences.
One idea could be that Towa uses her time - related powers to create an alternate timeline where she and Goku have to team up against a new, powerful enemy that threatens both their worlds. This would force them to work together and understand each other's powers better.
A possible plot could involve an evil force that targets Goku and Female Vegeta specifically because of their combined power. They are constantly on the run and have to rely on each other. In the process, they discover that their ki energies can be combined in a unique way. This discovery not only helps them fight the enemy but also deepens their bond as they realize how well they complement each other.