Another interesting concept is a crossover with the Harry Potter universe. Picture Kid at Hogwarts. He'd probably be a bit of a troublemaker, not fitting in well with the school rules. He could form an unlikely friendship with the Weasley twins and together they'd play pranks on the Slytherins, all while Kid is trying to find a way back to his own world.
If we consider a crossover with the Bleach universe, Ichigo could be paired with Kid. Ichigo is a soul reaper with a strong sense of justice. Kid, on the other hand, has his own pirate code. They could cross paths when some Hollows start attacking Kid's ship. At first, Ichigo might see Kid as a threat, but as they get to know each other, they could work together to defeat the Hollows.
The OC could be a pirate from a rival crew. They meet Kid during a battle. Instead of fighting to the death, they end up in a situation where they have to team up against a greater enemy. During this time, they get to know each other better, and a relationship between Kid and the OC starts to form.
One interesting Eustass Kid OC fanfiction could be about an OC who joins Kid's crew and has to prove their worth in various pirate battles. They might have a special power or skill that helps the crew in unexpected ways.
A cool Kaito Kid crossover fanfiction idea is with the world of Harry Potter. Kaito Kid could try to steal a magical artifact from Hogwarts, like the Philosopher's Stone. He'd have to navigate through the magical defenses and deal with the wizards and witches. Also, a crossover with One Piece. He might target a Devil Fruit, which would put him in conflict with the Straw Hat Pirates. And a crossover with Pokémon. He could be after a rare Pokémon that has some special power, like Mewtwo.
One idea could be a crossover with Harry Potter. Kid Goku could end up at Hogwarts and his martial arts skills would be a unique addition to the magical world. He might use his Ki blasts instead of magic spells in some situations.
One idea could be a crossover with the Teen Titans. Kid Flash could team up with them to fight a new super - villain that is causing chaos across multiple cities. His speed could add a new dynamic to the Titans' combat strategies.
One idea could be a crossover with the Dragon Ball Super universe. Kid Buu could encounter new and powerful foes like Jiren. Their fight would be chaotic and destructive, with Kid Buu's unpredictable nature causing all sorts of mayhem. Another idea is a crossover with the Naruto universe. Picture Kid Buu facing off against Naruto. Naruto's positive energy and willpower could be a contrast to Kid Buu's pure evil. He might try to reason with Kid Buu at first, but when that fails, a huge battle would ensue. And a third idea could be a crossover with the One Piece world. Kid Buu might land on the Grand Line and start causing trouble for the Straw Hat Pirates. Luffy would surely step up to protect his crew and the islands they visit from Kid Buu's rampage.
One idea could be that Kid and Kat end up in a strange new world together and have to work together to find their way back home, despite their usual rivalry. They could encounter all sorts of wacky creatures and challenges along the way.
One idea could be a crossover with other Lego themes like Ninjago. The Monkie Kid characters could team up with the Ninjago ninjas to fight a common enemy. For example, a powerful dark force that threatens both their worlds. They could combine their unique skills and powers, like Monkie Kid's staff skills and the ninjas' elemental powers.
One plot idea could be Kid Gilgamesh crossing over into a modern - day world and having to adapt to modern technology while still maintaining his pride and power. Maybe he gets into battles with modern superheroes who underestimate him at first.