Well, in the MHA manga, Dabi does meet his end. It's a poignant moment that has significant implications for the story's progression and the dynamics among the characters.
Midoriya Izuku could also have an interesting reaction. He's always trying to understand the villains better, and Dabi is a very mysterious villain. He might study the fanfictions to look for clues or insights into Dabi's character that he could use in a potential confrontation or in his quest to become a better hero. He might be surprised by some of the creative interpretations in the fanfictions.
A villain like Shigaraki would likely be interested in the power levels in the MCU fanfiction. He's always looking for ways to increase his own power, and seeing the various powerful artifacts and abilities in the MCU might give him some ideas. He could think about how he could use similar things in his own plans to take over the MHA world.
There are also cases where Shouto could be in shock. The suddenness of the kidnapping could leave him stunned for a while. During this time, Dabi could have the upper hand. But as Shouto recovers, his natural instincts as a hero trainee kick in, and he starts to think of ways to get free and stop Dabi's plan, whatever it may be.
Some MHA characters might be flattered. For example, Midoriya would probably be really excited and take it as a sign of how much he's inspired people. He might even look for positive lessons in the fanfiction to improve himself.
If the MHA characters were to react to a Mastermind fanfiction, some would be more accepting than others. Characters like Ochaco might find it really exciting. She's a fan of the heroes herself, so seeing different takes in fanfiction would be like getting a new perspective on the MHA world. However, characters like Shoto, who are more reserved, might be a bit hesitant. He might need some time to process what he's reading. But overall, it would be a very interesting scenario as it would show how the characters view different interpretations of their world.
Some characters would be shocked. For example, if the fanfiction had a really dark and unexpected Mastermind plot, like a hero turning out to be the mastermind of all the villains' plans, characters like Tsuyu would be very taken aback. She'd probably question the motives behind such a plot. Then there are characters like Denki. He might be more into it if it had some cool action scenes in the fanfiction, regardless of how out - of - the - blue the Mastermind storyline was. And Nejire would probably be super curious about the emotional depth of the characters in the fanfiction.
In such fanfiction, Touya might be depicted as a strong - willed character, perhaps with a bit of mystery. Sakura could be shown as kind - hearted yet with her own inner strength. However, these characteristics can vary greatly depending on the author's interpretation.
If it's a Disney fanfiction based on a princess story, the female characters in MHA like Momo Yaoyorozu might relate to the princesses' grace and leadership. Meanwhile, the male characters could either be in awe or a bit dismissive, depending on their personalities. For example, Todoroki might be quietly respectful, while Mineta might make some inappropriate remarks (if we're being honest about his character).
MHA characters might also be a bit jealous of some of the superpowers or unique abilities in other anime fanfiction. In their world, quirks are relatively well - defined, but in some other anime, there are really out - of - this - world powers. They could be in awe of the creativity and at the same time, try to figure out how they could incorporate some of those ideas into their own fighting styles. Like, if they read a fanfiction about a character who can manipulate time, they might start thinking about how they could use their quirks in a time - related way.