The plot could involve a villain from One Piece using the power of bending against the world of Korra. For example, Blackbeard discovers a way to steal bending abilities and starts causing chaos. Korra, in her quest to stop him, meets the One Piece crew who are also affected by Blackbeard's actions. Together, they combine their skills, with Korra's bending and the Straw Hats' various fighting styles and Devil Fruit powers to take on Blackbeard.
It could be amazing. Maybe Luffy and his crew end up in the Avatar world. Luffy might be intrigued by the bending powers and try to learn them in his own goofy way. Zoro could have a sword - fighting duel with some of the best benders. And Nami would probably be interested in the unique treasures and cultures of the Avatar world.
Zoro's swordsmanship could interact well with earthbending. Earthbenders could create structures for Zoro to jump off of and gain more momentum for his attacks. His three - sword style could be adapted to work with the flow of earth or water if he were to fight alongside benders. As for Sanji, his kicks could be combined with firebending techniques. He could use the heat generated by a firebender to increase the power of his Diable Jambe kicks. And the Straw Hats' Haki could also play a role, perhaps being able to sense the presence of benders or even disrupt their bending abilities in some cases.
It could be Brook. A skeleton in the Avatar world? He'd be a total anomaly. His music might have strange effects on the bending elements. He could also tell the Avatar characters stories about his past life and his adventures with the Straw Hats. The Avatar characters would be both fascinated and a little creeped out by him.
One possible plot could be that the Straw Hat Pirates end up in the Fairy Tail world due to some magical anomaly. They team up with the Fairy Tail guild to fight a common enemy like a powerful dark wizard who has the power to control the seas as well. Luffy and Natsu could have a friendly competition about who is stronger while their respective crews and guild members learn from each other's fighting styles.
Well, it could be about the Straw Hats accidentally ending up in the Marvel universe. They meet the Avengers and at first there's some misunderstanding because of their different ways. But then they realize they can work together. Maybe Luffy is fascinated by Thor's hammer and tries to lift it, while Zoro wants to have a sword fight with Captain America's shield.
A Legend of Korra and Star Wars crossover would likely have some really cool character interactions. Aang's spirit could meet Yoda's. They could share their wisdom about the balance of the universe. Also, the technology from Star Wars like lightsabers and starships would be fascinating to see in the world of Legend of Korra. How would the people of that world react to such advanced technology? It could lead to some great storylines about adaptation and progress.
Perhaps he's reincarnated as an avatar - like figure, not exactly the avatar but with some special connection to the spirit world. He then has to use this connection to help restore balance in the world. He might encounter different spirits, some friendly and some hostile, and has to find a way to co - exist with them while also dealing with the human problems in the story.
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.