One interesting plot idea could be that Frieza somehow manages to gain new powers on a distant planet and returns to challenge Goku again. But this time, instead of just brute strength, he uses cunning strategies. Another could be a scenario where Goku and Frieza are forced to team up against an even greater threat from another universe. This would be a great chance to explore their complex relationship.
A possible plot idea is a time - travel fanfiction. What if Frieza went back in time and tried to prevent Goku from ever becoming a Super Saiyan? He could change key events in Goku's past, like interfering with his training under Kami or Master Roshi. Then Goku would have to find a way to regain his power and face Frieza in this altered timeline.
One idea could be Goku Jr facing a new, powerful enemy that has a unique power related to time manipulation. This would force him to train in ways he never has before and seek help from unexpected allies, like some of the older, wiser characters from the original Dragon Ball Z series.
One idea could be Goku and Gohan going on a special training journey to a new planet with unique gravity and energy sources. This would force them to adapt and develop new techniques together.
A plot could involve Bulma creating a new device that Goku needs to use in order to defeat an extremely powerful enemy. Goku has to learn how to operate this device with Bulma's guidance, and they face many obstacles along the way. This would show their cooperation and how their different skillsets complement each other. It could also lead to some comical moments as Goku tries to understand the complex technology. Another interesting plot could be that they are both transported to an alternate dimension where the rules of the Dragon Ball world are slightly different. They have to figure out how to adapt and find a way back home while also uncovering the secrets of this new dimension.
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.
One interesting plot idea could be Goku training Caulifla in a new form of Ultra Instinct. This would allow for a deep exploration of their mentor - mentee relationship. Caulifla is already a strong fighter, but with Goku's guidance, she could reach new heights. Another plot could involve them teaming up against a powerful new enemy that neither could defeat alone. They'd have to combine their unique fighting styles and powers to win.
One idea could be that they have to team up in a new and strange way due to a unique threat. Maybe there's a villain who can only be defeated by a special combination of their powers that they discover through their new 'mate' relationship. For example, they might have to combine their ki in a way they've never done before.
One idea could be that Female Goku and Vegeta have to team up to save the universe from a new and powerful enemy. They start off not getting along well, like in the original series, but as they face challenges together, they develop a mutual respect and friendship.
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 Goku traveling back to the Saiyan - Planet Vegeta days. He could try to prevent the destruction of the planet by Frieza. Maybe he'd train with his father Bardock and change the power dynamics among the Saiyans. Another plot could be Goku going to the future to meet his descendants and see how they've carried on the Saiyan legacy. He could also time travel to key moments in his own battles, like going back to his fight with Vegeta on Earth and using his future knowledge to end the fight more quickly.
One interesting 'Dragon Ball Z TG Frieza' fanfiction could be one where Frieza has a character transformation that makes him question his evil ways. For example, he might be exposed to the kindness of the Earthlings and start to have a change of heart.