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.
I don't have enough context to determine exactly who 'garp' is. It could be a newly created character by the fanfic writer, or it might be a character from a relatively unknown story that is being incorporated into the 'ace fanfic'.
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.