Goku from Dragon Ball Z could be a great crossover character. Goku's super - strength and fighting skills could match up well with Katakuri's powers. They could have an epic battle or, perhaps, learn from each other's fighting styles and philosophies.
Luffy from One Piece would be an obvious choice. Their relationship in the original One Piece story is already complex and full of potential for more exploration in a crossover fanfiction. They could team up in a different universe or be forced to fight against each other in a strange new setting.
Saitama from One - Punch Man would also make for an interesting crossover. Saitama's seemingly invincible strength contrasted with Katakuri's more strategic and predictive fighting style could lead to some really funny and action - packed scenarios in a fanfiction.
Superman from the DC universe. Superman stands for truth, justice, and the American way, but his methods are often more lenient compared to Akainu. The two could have a philosophical debate about justice while also having to fight a common enemy.
One popular type of OC is a female pirate who is as strong - willed as Katakuri. She challenges him in a battle of wits and strength, and their interactions create a lot of tension and intrigue in the fanfiction. For example, she might try to steal a precious treasure that Katakuri is guarding.
Luffy from One Piece could be a great crossover character with Deidara. Luffy's carefree and adventurous nature would contrast with Deidara's more artistic and destructive tendencies. They could start off as enemies, with Deidara seeing Luffy as a target for his art, but then end up as reluctant allies when facing a common threat.
Luffy from 'One Piece' would also be an interesting crossover character. Imagine Ichigo being abandoned on an island in the 'One Piece' world. Luffy's carefree yet determined nature could contrast with Ichigo's more brooding personality. They could embark on a journey together, with Ichigo learning about the concept of the 'One Piece' and using his powers in unexpected ways within this new world.
Kakashi from Naruto himself could be part of a 'grey' themed crossover within the Naruto universe. Maybe a situation where Kakashi's past and his more mysterious side are explored further, and Naruto has to work with him in a darker, more complex mission that delves into the grey areas of the ninja world.
Alice from Alice in Wonderland could also be an interesting choice. Her curious nature would lead her to explore the world of Young Dracula. And Young Dracula might be both amused and a bit annoyed by her constant questions and her fearless attitude in the face of his vampiric self.
Piccolo could be an interesting crossover character. He could be from a world where lemons have some sort of magical or spiritual significance. His relationship with Gohan in the original story would add depth to their interactions in this crossover. For example, Piccolo might be initially skeptical of the lemon - related things but eventually see their value when it comes to helping Gohan.
Solid Snake from the Metal Gear series would be a great choice. His stealth skills and military expertise would contrast with Travis Touchdown's more brash and direct fighting style. They could be forced to work together on a mission, and learn from each other's ways of combat.
Goku from Dragon Ball Z could be an interesting crossover character. His raw power combined with Sasuke's strategic use of the Rinnegan could make for some amazing battles and interactions. They could learn from each other's fighting styles.
I think Deadpool would be a great crossover character with Johnny Gat. They both have a crazy sense of humor and are not afraid to get into some wild and violent situations. Their banter would be hilarious as they fight side by side against bad guys.