Well, consider a fanfiction where an experiment gone wrong turns Goku into a pet - like form. Vegeta, being the proud Saiyan he is, initially mocks Goku but then starts to take care of him. As time passes, Goku starts to regain his normal form bit by bit. This creates a complex relationship between them. Or there could be a story set in a world where there are different social hierarchies among Saiyans. Goku, being from a lower caste, is made Vegeta's pet. However, their bond gradually changes as they face common enemies and challenges together, defying the initial pet - owner relationship.
In some fanfiction, perhaps Goku gets cursed by a powerful enemy. This curse makes him lose his human - like intelligence and abilities, and he starts behaving more like an animal. Vegeta, instead of killing him, decides to keep him as a pet. Maybe he wants to study Goku in this state or he just feels some strange sense of responsibility. Another storyline could be that Vegeta discovers a way to control Goku's mind and uses it to make Goku his pet, but as the story progresses, Vegeta starts to feel guilty about it.
In some fanfictions, it might be a really strange and unique concept where Goku is depicted as Vegeta's pet. But this is far from the original relationship in the official Dragon Ball story. It's just a creative and often humorous take that some fanfic writers explore.
One possible plot could be that Goku is under some sort of mind - control and ends up abusing Vegeta. Another could be in a dark, alternate universe where Goku's character has been twisted and he sees Vegeta as a threat to be eliminated rather than a rival. Maybe there could also be a plot where Goku is tricked into believing Vegeta has done something unforgivable and so he takes out his anger on him.
In 'Goku betrayed fanfiction', a common plot might be the corruption of his power. Let's say Goku discovers a new form of power that is seen as too dangerous by others. His friends and even some of the Z - fighters fear that he'll lose control and turn on them. So they decide to betray him first to protect the Earth. Another aspect could be a political betrayal. If there were some sort of intergalactic politics involved, Goku might be sacrificed or betrayed by his own side to make a deal with a more powerful alien race. And then there's the idea of a time - travel - related betrayal. Maybe someone from the future comes back and convinces everyone that Goku will cause a great disaster in the future, causing them to betray him in the present.
Maybe in the fanfiction, Vegeta and Bulma decide to go on a second honeymoon. During this time, they encounter an old enemy who has a new vendetta against Vegeta. They have to work together, using Vegeta's strength and Bulma's intelligence, to defeat the enemy and in the process, their bond becomes even stronger. It could also show how they support each other's dreams, like Bulma's inventions and Vegeta's pursuit of greater power.
If Tatsumi is Esdeath's pet in fanfiction, there could be a storyline where Tatsumi is forced to participate in Esdeath's cruel games. He might be made to fight other 'pets' or perform dangerous tasks for her amusement. Or, perhaps Tatsumi tries to use his position as her pet to gain information and eventually turn the tables on Esdeath, leading to a plot full of intrigue and suspense.
Perhaps in a fanfiction, Bulma discovers a new side of Vegeta when they are on a trip together away from the chaos of their usual lives. This new side makes her see him in a different light and they end up expressing their love physically. Also, it could be that Vegeta, who is usually stoic, finally lets his guard down completely around Bulma due to some life - threatening situation they overcome together.
One possible storyline could be that Goku gets Ultra Instinct right when Frieza is about to kill all the Namekians. He then uses his newfound power to completely overpower Frieza and save the day. Another could be that he gets it during a battle with the Ginyu Force and easily defeats them all in one go.
It's possible that Vegeta would gain a new respect for Goku. By seeing Goku's memories, he gets to understand the full scope of Goku's life, his struggles, and how he overcame them. This could lead Vegeta to view Goku in a different light and perhaps even strengthen their rivalry in a more positive way.
One possible storyline could be that Vegeta, being the tough and proud Saiyan, initially clashes with Bulma in high school. Maybe he doesn't understand her scientific genius and sees it as a waste of time at first. But as they are paired for a project, he starts to see her determination and intelligence in a new light. Another could be that Bulma is intrigued by Vegeta's otherworldly strength and tries to study him, which he initially resents but later warms up to as they get to know each other better. And a third storyline might be that there is a school competition, and Vegeta's combat skills and Bulma's technological know - how combine to make their team unbeatable.
One possible storyline could be Naruto using his ninja skills to protect Ruby from the Grimm. His ability to move stealthily and use jutsus could give Ruby an edge in combat.