Well, a possible plot could be that Goku and Vegeta are in different high school cliques. Goku is with the friendly and outgoing group, and Vegeta is in the more serious and studious clique. However, a school event forces them to interact. They initially clash due to their different personalities and ways of doing things. But then, they find out they both have a shared goal of protecting the school from a hidden threat. This makes them put aside their differences and combine their powers. Or perhaps they both have a crush on the same girl in high school, and they compete in a friendly way to win her heart, which also leads to some character growth for both of them.
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.
Maybe there could be a story where Android 18 gets sent to a different dimension and Goku and Vegeta have to follow her to bring her back. In this dimension, the rules of power and fighting are different. They all have to adapt quickly. Goku and Vegeta might learn some new skills from Android 18 as she has a different way of approaching combat situations due to her android nature.
Maybe a fanfiction where in an alternate universe, Goku, Chichi and Vegeta are part of a special council that governs the Saiyan race. They have to deal with political issues as well as threats from outside forces. This would explore their different personalities in a new context. Goku's laid - back nature, Chichi's strong - willed attitude and Vegeta's pride all play a role in the decision - making process.
One idea could be that Goku and Vegeta are transported to an alternate universe where they have to team up with their alternate selves to defeat a powerful new enemy that is a combination of all the foes they've ever faced. This would force them to not only work together but also understand different versions of themselves.
Maybe in the fanfiction, Goku and Fem Vegeta start a harem as a way to train stronger fighters. They bring in various characters from different planets and train them in their unique ways. Along the way, romantic feelings start to develop between the members of the harem and Goku and Fem Vegeta have to deal with the resulting jealousies and rivalries.
One idea could be that Goku and Vegeta travel back in time to the Saiyan - Planet. They could try to change the fate of the Saiyans, like preventing Frieza from destroying their planet. This would bring a whole new set of challenges as they would have to deal with the Saiyan culture and politics of that time.
One idea could be that Female Vegeta and Goku are forced to team up for a special mission. They start off bickering as they usually do, but as they face challenges together, they begin to respect each other's fighting styles more. Maybe they have to battle a new, extremely powerful enemy that neither could defeat alone. This situation could lead to some interesting character development and a budding friendship or something more.
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.
A possible plot could be that they are transported to a parallel universe where male Saiyans are able to get pregnant. They meet alternate versions of themselves and their friends, and have to adapt to this new world while dealing with their pregnancy. This could lead to many adventures and self - discovery moments for both of them.
Perhaps a fanfiction where Vegeta and Goku get transported to an alternate universe. In this universe, their roles are reversed, and they have to adapt to the new situation while still trying to find a way back home. They would face challenges that are unique to this new world and learn from each other in different ways.