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.
One possible plot could be that there is a rift in the multiverse that brings Goku and Luffy together in a strange new world. They initially misunderstand each other and start to fight. As the fight progresses, they both realize that there is a greater threat at hand that is causing the rift. So, they team up, with Goku teaching Luffy some of his combat techniques and Luffy showing Goku the value of friendship and loyalty in a different way.
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.
Goku in Ultra Instinct mode is extremely powerful. He has superhuman speed, strength, and can dodge attacks effortlessly. However, Luffy also has his own set of amazing abilities like his Gear Fourth form which gives him enhanced speed and power. But I think Goku would win because his combat skills and power level are just on a different scale compared to Luffy.
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.
The theme of acceptance is quite common. Fem Luffy often has to be accepted by the other characters in the story. This could be because she's different due to her gender or her slightly different personality traits. Also, the theme of self - discovery is prevalent. As fem Luffy navigates the pirate world, she discovers more about herself, her abilities, and her place in the grand scheme of things.
Nami could also be a common character. She might help Luffy manage the financial aspects of his admiral duties, as well as use her navigation skills to assist in any navy - related voyages. And of course, she'd be there to keep Luffy in check when he gets too carried away.
Rayleigh would be a great candidate. He's an experienced pirate and has already trained Luffy for a while. He has a lot of knowledge about the world of pirates and could give Luffy a talk about the deeper secrets of the Grand Line or how to deal with the powerful enemies that lie ahead.
One popular luffy and fem luffy fanfiction is 'Fem Luffy's Adventure'. It shows a different side of Luffy if she was a female, with unique storylines and character developments. Another one could be 'Fem Luffy in a New World' which explores how fem Luffy might interact with the other characters in the One Piece world in new and interesting ways.