A great fanfiction could be Whis falling in love with a new character. This new character might be a powerful being from a different galaxy. Their relationship would bring a whole new dynamic to the story. Whis would have to balance his duties as an attendant to Beerus with his new - found feelings. Also, there could be a story where Whis creates a new form of training for Vegeta that helps him finally surpass Goku in power, which would be a huge twist in the Dragon Ball Super narrative.
Some fanfictions focus on Whis exploring the multiverse. He could discover different versions of the Dragon Ball characters in other universes. Maybe in one universe, Goku is a villain and Whis has to figure out how to deal with this alternate Goku. Or he could find a universe where there is a new and more powerful form of the Dragon Balls that he tries to bring back to his own universe for some reason, like to prevent an upcoming catastrophe.
Obviously, Whis is a main character in most of these fanfictions. He is often the center of the story, whether it's about his powers, his relationships, or his role in the Dragon Ball Super universe. Goku also frequently appears in these stories. Since Goku is always eager to learn and become stronger, Whis is often his mentor in fanfictions, so their interactions are a common theme.
There are fanfictions that focus on the relationships between the characters. For example, a story where Vegeta has to team up with Frieza in an alternate universe to fight a common enemy stronger than both of them. This forces Vegeta to put aside his hatred and work with his old foe, creating an interesting dynamic.
A great fanfiction idea is a fusion of the power systems. For example, a story where characters can combine chakra and ki. Naruto could try to use ki - enhanced rasengan or Goku could use a chakra - based Kamehameha. It would be an exciting exploration of both universes' power concepts.
Another great 'Broly Dragon Ball Super Fanfiction' could revolve around Broly's past on Planet Vegeta. What if there were more secrets about his family? Maybe he had a sister or a brother who was also extremely powerful but was lost during the destruction of the planet. This fanfiction could explore Broly's search for his lost family member while still dealing with the threats in the present universe.
One interesting story could be about a new villain who forces Goku to reach the SSJ4 form in a completely different way. Maybe he has to combine his Saiyan powers with some ancient energy source on a new planet. Another could be a fanfiction where Vegeta finally masters the SSJ4 form before Goku and has to face a powerful foe alone.
One interesting fan theory is about the potential hidden powers of some minor characters. For example, some think that Yajirobe might have a secret super form that was never revealed in the original series. It's just a fun idea that fans like to explore in fanfiction.
In Dragon Ball Super Super Saiyan 4 fanfiction, often there are concepts about alternate universes. Picture a universe where Super Saiyan 4 is the norm rather than an extreme form. This could lead to different power hierarchies and battles. Additionally, some fanfictions explore the idea of Saiyan - human hybrids achieving Super Saiyan 4 in unique ways, perhaps with abilities that are a blend of human ingenuity and Saiyan strength.
Another interesting plot could be about Vegeta finally achieving a power level that surpasses Goku in a completely unexpected way. For example, through a unique form of meditation or a new type of training regime that he stumbles upon. This could lead to a whole new dynamic in their relationship and in the battles they face.
One interesting storyline could be Android 21's struggle to find her true identity. In fanfiction, she might discover that she has a hidden past or purpose that was not initially known in the original series.
A great 'Dragon Ball Super Crossover Fanfiction' concept might involve a crossover with the Harry Potter world. The Saiyans could visit Hogwarts. Maybe Vegeta could be really intrigued by the magic there and try to learn some spells, while at the same time the wizards are in awe of the Saiyans' power. There could be a dark wizard who wants to use the Dragon Balls for his own evil purposes, and the Hogwarts students and the Z - fighters have to work together to stop him.