The unique aspect is that it combines the familiar characters of One Piece with the concept of reaction. It's fun to see how characters like Luffy or Zoro would react to things they might not have known before, like modern technology or different interpretations of their own stories.
Some would be excited. Luffy would probably be eager to jump into the future he sees in the fanfiction. He's always looking forward to adventures, and if the future seems cool, he'd be all for it.
Sure. 'One Piece: The Straw Hats React to Their Future' is a great one. It shows how the Straw Hat crew reacts to seeing possible future events of their adventures, which is really interesting.
They may laugh out loud if there are humorous parts in the fanfic. For instance, if the fanfic writer creates a comical situation involving the characters that is well - written.
They might be shocked. Luffy's Gear 5 is such a powerful and strange form. In the fanfiction, characters could be amazed at his new abilities, like his cartoon - like movements and seemingly limitless power.
Luffy would be really emotional. He might laugh at the funny parts of Ace's past and cry at the sad ones. He loves his brother so much that any story about Ace would have a big impact on him.
They might be shocked. Luffy has so many wild and dangerous adventures in his memories. His friends would probably be in awe of how much he has endured and how strong his will is.
Superman may see the similarities in the heroism of the One Piece characters to his own. However, he'd also notice the differences in how they achieve their goals. He might think about how he could incorporate some of their fearless attitudes into his own battles back home. Batman would be very observant. He'd study the motives of the villains in the One Piece fanfiction and how the heroes counter them, and might even get some new ideas for dealing with Gotham's rogues.
Sanji would go all out in cooking the most nutritious and delicious meals for Usopp to help him recover. He might also be a bit overprotective, not allowing anyone to disturb Usopp while he's eating. Chopper would be in full - on doctor mode. He'd be constantly checking Usopp's vital signs, giving him medicine, and trying to figure out the cause of the sickness. Robin would be quietly researching any possible cures or causes, using her knowledge of history and ancient texts.