In a crossover fanfiction, it could be that the power of Devil Fruits from One Piece becomes known in the Dragonball universe. Vegeta, being his prideful self, wants to obtain a Devil Fruit power to make himself even stronger. He travels to the One Piece world and accidentally ends up on the Thousand Sunny. The Straw Hat crew initially see him as a threat but then realize they can help each other. They end up in a big adventure together where they combine their powers to fight a new common enemy that threatens both universes.
Another plot could involve the Devil Fruits from One Piece and the Ki powers in Dragonball. For example, a character could eat a Devil Fruit that gives them the ability to manipulate Ki in a unique way. Or perhaps a Dragonball character accidentally eats a Devil Fruit while visiting the One Piece world and has to deal with the consequences, like not being able to swim.
One interesting plot could be that the Pokemons are suddenly exposed to the energy of the Dragon Balls. Some Pokemons start to gain Saiyan - like abilities. For example, Pikachu could become Super Saiyan Pikachu, with its electric powers amplified to an extreme level. It could then face off against powerful Pokemon villains in a whole new way, with the fast - paced combat style of Dragonball Z.
Well, maybe the Omnitrix gets damaged and its energy somehow mixes with a Devil Fruit. This creates a new situation where Ben has to deal with having powers from both the Omnitrix and the Devil Fruit. And the Straw Hats are intrigued by this new power source and try to help Ben control it while also facing threats from other pirates who want this power for themselves.
One possible plot could be Itachi arriving in the One Piece world and being mistaken for a powerful new pirate. The Straw Hats might initially be cautious but then realize his skills could be useful. Itachi, with his Sharingan, could help them in battles against the World Government or other strong enemies. For example, his genjutsu could be used to deceive opponents during sea battles.
One idea could be that the Straw Hats end up in the Naruto world. Luffy might befriend Naruto and they could team up to fight a common enemy like Akatsuki members who are after some powerful Devil Fruits that have mysteriously appeared in the Naruto world. Zoro could have duels with some of the skilled sword - users in the Naruto universe, like Sasuke or Killer Bee when he uses his sword - like Samehada.
Perhaps there's a powerful and mysterious treasure in the RWBY world that the Straw Hats hear about. It could be something related to the Dust or an ancient relic. They team up with the RWBY characters to search for it. Along the way, they encounter various villains from both universes who also want the treasure. Ruby's speed and Crescent Rose could be compared to Usopp's long - range attacks, and Blake's stealth could be useful in sneaking past enemies. The story could explore how the different powers and personalities interact during this adventure.
One possible plot could be that the Straw Hat crew sails to the world of Sekirei. Luffy might be intrigued by the concept of Sekirei battles and try to participate in a friendly way. Maybe Zoro would find some Sekirei with interesting sword - fighting skills and have duels with them. And Nami could be interested in the economic aspects of the Sekirei world, like how they trade resources or manage their finances.
Zoro and Vegeta would also have a great interaction. Zoro, with his strong sense of honor and his goal of becoming the world's greatest swordsman, would be a worthy opponent for Vegeta. Vegeta would be interested in Zoro's swordsmanship and might even see him as a potential rival. They could have some intense training sessions together, sharing their knowledge of combat and power - up techniques.
Well, in a One Piece and Dragonball Z crossover fanfiction, the art styles are quite different, but that could add to the charm. For example, the colorful and outlandish characters from One Piece would contrast with the more muscular and intense look of Dragonball Z characters. Maybe the Straw Hat crew would be intrigued by the Dragon Balls and their power to grant wishes. They could embark on a journey to find all the Dragon Balls, while also dealing with the likes of Cell or Majin Buu who are interested in their unique abilities.
One possible plot could be that the Sailor Scouts are facing a new and extremely powerful enemy that they can't defeat on their own. Goku and his friends from Dragonball Z sense the danger across the dimensions and come to help. The Scouts are initially shocked by the Saiyans' power levels but then start to learn from them about ki control. Together, they combine their powers, like the Sailor Scouts using their magic with the Z - fighters' ki blasts to take on the foe.