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.
In the 'ichigo gets hypnotized fanfiction', he might start acting in ways that are out of character. For example, he could be made to fight against his friends under the influence of hypnosis.
Team Rocket is an obvious choice. They could use some new, devious hypnosis device to control Ash for their own gain, like trying to steal all his Pokémon.
In 'sonic gets hypnotized fanfiction', a prevalent theme could be the exploration of Sonic's mind. How does the hypnosis affect his thoughts, memories, and actions? Another theme might be the power dynamics. The one who hypnotizes Sonic has a certain power over him, and this can create tension and conflict. Additionally, the fanfiction may touch on themes of friendship as Sonic's friends come to his rescue and try to break the hypnosis.
It could be about Luffy having an important conversation. Maybe it's about his dreams, his crew, or some kind of revelation he has. Without reading it, it's hard to say exactly.
I'm not sure if there is such a specific fanfiction. There are a vast number of fanfictions out there, but this particular concept might be quite rare or not in line with the general tone of the 'One Piece' series. Fanfiction often explores different relationships and scenarios, but this one seems rather out - of - the - ordinary considering the nature of the characters in the original work.
Finding 'sonic gets hypnotized fanfiction' can be an interesting search. Fanfiction often explores unique and unusual concepts like this. You might have to dig a bit deeper. Start with general Sonic fanfiction communities. Sometimes, the stories might not be directly tagged with 'hypnotized' but could still have elements of it in the plot. So, read the summaries carefully when you're browsing through the available fanfictions.
A third theme could be facing greater challenges. In these fanfictions, the challenges are so big that Luffy can't just rely on his normal, laid - back self. He has to be more serious to overcome them.
In this fanfiction, Luffy might be used as a bargaining chip by his captors. Maybe they'll try to exchange him for something valuable, like a powerful Devil Fruit or a large amount of treasure. His crew would then surely launch a rescue mission, facing many challenges along the way.