Well, in a lot of fanfictions about Luffy vs Katakuri, Luffy's growth is depicted quite vividly. His growth can be seen in his improved observation Haki. He starts to anticipate Katakuri's attacks more accurately, which is a huge step forward. He also becomes more creative with his attacks. Instead of just using his standard punches and kicks, he combines different moves and even creates new ones on the fly. This shows that he's evolving as a fighter and not just relying on his basic skills. Another aspect is his mental growth. He faces a very tough opponent in Katakuri, but he doesn't give up. His resolve gets even stronger, which is an important part of his overall growth in these fanfictions.
The "Negative Fruit" in One Piece was one of the superpowers that Luffy encountered for the first time in the story. The scene where Luffy and his gang fought against the "Negative Fruit" appeared in episode 598,"Luffy and Luffy!" Adventures in Two Worlds.
One of the most exciting moments could be when Luffy first uses his new gear or technique that surprises Katakuri. It shows Luffy's growth and adaptability in the fight. Another exciting part might be when Katakuri reveals a new form or power that Luffy has to quickly figure out how to counter. This back - and - forth of power display and strategic thinking keeps the 'fanfiction' action - packed.