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 a few novels that I can recommend to you. They are all stories about being reborn as a Demon Slayer. The first was "Rebirth of the Sea of Laws, I Slay Demons in the Human World" and "Rebirth of Slaying Demons, I Actually Became a Demon Venerable?" They all focused on slaying demons and told the story of the protagonist becoming a demon slayer after his rebirth. In addition, there was also "Xu Xian's Demon-slaying Daily Life (Demonic Meow)" and "Black Moonlight of the Rebirth of the Demon Lord," which also involved the demon-slaying plot. These novels all have different styles and storylines. You can choose to read them according to your preferences.
Definitely! Demon Slayer started as a manga. It's known for its compelling plot and well-developed characters. The manga provides the foundation for the success of the anime adaptation.
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.