Usopp might be inspired to be braver. When he watches Luffy's memories, he could see how Luffy fearlessly faces powerful enemies. This would make Usopp want to overcome his own cowardice and be more like Luffy. And Robin, she would gain more insights into Luffy's kind heart. She might see how Luffy has always been inclusive and accepting of everyone, which would make her feel even more at home in the crew.
When Hogwarts watches Harry's worst memories, Neville would find inspiration in Harry's ability to persevere. He might see that his own insecurities are nothing compared to what Harry has faced. Luna would have her own unique perspective. She might see the beauty in Harry's ability to hold on to hope even in his worst memories. The Hufflepuff students would be empathetic and might offer Harry small acts of kindness like making him special treats or leaving him encouraging notes around the school.
They would probably be very emotional. Some of them might cry, especially Molly, seeing all the pain Harry has been through.
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.
They might gain a deeper understanding of his motivation and growth. For example, Zoro could see how Luffy's dreams have evolved over time, which would strengthen their bond even more.
Some characters might be critical. Elsa, being a powerful and responsible character, might not like it if the fanfiction misrepresents her in a way that goes against her values. She might think that the writers should be more respectful of her character arc and not make her do things that are completely out of character just for the sake of a wild story. However, at the same time, she might also appreciate the creativity in some parts.
Some would be intrigued. Captain America, being an open - minded person, might be interested in seeing different interpretations of their team dynamics. He could even gain new insights about his relationships with his fellow Avengers through the fanfiction.
The cynical characters might be critical. They could pick apart the plot holes or the unrealistic elements in the fanfiction. They might say things like 'This doesn't make any sense compared to the real Grinch story.'
They'd be shocked and maybe even emotional. Discovering each other's hidden thoughts and past experiences could lead to a deeper understanding and stronger bonds among them.
Metro Man might be more laid - back about it. He'd probably see it as a fun take on their world and might even chuckle at some of the more outlandish interpretations of their battles and relationships. He could also use it as a chance to better understand how the public perceives them both.
Hero characters might analyze it from a moral perspective. They could either approve or disapprove of the way the story is told in the fanfiction depending on whether it aligns with their sense of right and wrong. Villain characters, on the other hand, might look for ways to use the ideas in the fanfiction to their advantage, like new ways to create chaos.