It could be about a fan - created story in the My Hero Academia (MHA) universe where Bakudeku (presumably a relationship or dynamic between Bakugo and Deku) are involved with a secretary agency. Maybe they work there, or the agency has something to do with their hero activities.
You can try looking on fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. They have a large collection of My Hero Academia fanfics, and you might be able to find the 'bakudeku secretary agency mha fanfic' there.
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.
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.
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.
Bakugo might initially be in denial. He's always had a complex relationship with Izuku, and seeing him in such a state could shatter his world view. He might become more withdrawn or, on the contrary, be spurred into a violent rage against whoever was responsible.
Well, Bakugo might scoff at first. He'd probably think Batman is too brooding and not as straightforward as he likes his heroes. But then as he reads more of the fanfiction, he might grudgingly admit that Batman's detective skills are cool. Deku, on the other hand, would be super interested. He'd be analyzing every move Batman makes in the fanfiction, taking notes in his head about Batman's strategies and how they could be applied in his own hero work. Uraraka would be more focused on the relationships in the fanfiction. She'd be all 'aww' at the cute moments and feel for the characters when they're in trouble.
It could start with Hinata's small acts of kindness that Naruto begins to notice more. For example, she might always have his favorite food ready when they accidentally meet. This makes Naruto curious about her feelings, and gradually they start to have more private conversations.
Well, Dez could be the kind of friend who is always in his own little world. So he doesn't really pick up on the fact that Austin and Ally are secretly dating. But Trish is different. She's more in tune with what's going on around her. She might start to see the small changes in their behavior, like how they seem to be more protective of each other. She might be a bit suspicious and start to keep a closer eye on them, which could add a lot of tension to the story as Austin and Ally try to keep their relationship under wraps.