A cool fanfiction concept would be a tournament where characters from both Dragon Ball Super and Naruto universes participate. It would be exciting to see how Naruto's clones would fare against Goku's Instant Transmission or Vegeta's Galick Gun.
One idea could be a story where Goku and Vegeta from Dragon Ball Super end up in the world of Dragon Ball GT by some sort of time - space rift. They then have to team up with the GT versions of themselves to fight a new, powerful enemy that is threatening both timelines.
One idea could be that a character from Naruto's world somehow gets transported to the Dragon Ball Super universe and ends up in a harem situation. For example, Naruto himself could be sent there and due to his unique abilities and charm, attract the attention of various female characters like Bulma, Android 18, and Chi - Chi. Another plot could involve a new villain who uses the concept of a harem to manipulate characters from both universes, forcing them to work together to overcome this strange threat.
One idea could be exploring an alternate timeline where Kai was the main protagonist instead of Goku. He could have unique training methods and face different villains.
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.
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.
Well, for 'Dragon Ball Super GT fanfiction', you could write about a new villain that is more powerful than any they've faced before. This villain could be from a long - lost part of the universe. You could also do a story where the Z - fighters have to train in a completely different way, like learning magic instead of just martial arts. Or a fanfic about the Saiyan race's origin in more detail than what was shown in the series.
One idea could be creating an OC (Original Character) who is a Saiyan from a long - lost branch of the Saiyan race. This OC could have unique abilities that are a blend of traditional Saiyan powers and something new, like the ability to manipulate energy in a very different way. Maybe they can turn their ki into a solid form for various combat uses.
One interesting crossover could be a battle between Naruto's Rasengan and Goku's Kamehameha. It would be epic to see the different energy forms collide. Maybe Naruto could learn some of Goku's training techniques and vice versa, like Naruto trying to achieve Super Saiyan levels of power or Goku learning about chakra control.
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.
One idea could be to insert yourself as a new Saiyan character. You could have unique powers, like the ability to control a new type of energy. Maybe you arrive on Earth during the Tournament of Power and form an unexpected alliance with Goku and the others. Another idea is to be a non - Saiyan with a special gadget that can nullify ki attacks, which would create really interesting battle scenarios in the Dragon Ball Super universe.