Luffy fights Katakuri in Episode 851 of the One Piece anime, titled "The Man with a Bounty of Billion – The Strongest Sweet Commander, Katakuri". The confrontation between Luffy and Katakuri begins in Episode 851 and continues on to Episode 852, titled "A Hard Battle Starts – Luffy vs. Katakuri". The fight ends in Episode 871, titled "Finally, Its Over! The Climax of the Intense Fight against Katakuri!". Therefore, the fight between Luffy and Katakuri lasts for a total of 21 episodes, from Episode 851 to Episode 871.