I really like the fan fiction 'All Might: The Early Days'. It delves into All Might's backstory, exploring how he got his powers and the challenges he faced before becoming the symbol of peace. It gives a deeper understanding of his character.
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 He might become more withdrawn or, on the contrary, be spurred into a violent rage against whoever was responsible.
One common theme is mentorship. All Might is Deku's mentor, so a lot of fanfics explore how he guides Deku, like teaching him how to use his power effectively.
Archive of Our Own (AO3) is also a great place. It has a large collection of fan fiction, including many about All Might. The tagging system makes it easy to find exactly what you're looking for in terms of genre, length, and more.
One great fanfic could be 'All Might's Legacy' which beautifully explores the relationship between All Might and Deku. It shows how Deku grows under All Might's mentorship and the emotional bond that forms between them.
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.
Reader angst fanfic typically involves stories where the reader inserts themselves into a fictional scenario and experiences angst. It could be angst related to relationships with characters, difficult situations in the fictional world, or emotional turmoil within the story.
In a 'branch angst fanfic', the 'branch' could be a metaphorical one. Say, in a fanfic based on a fantasy world, a character's magical powers start to develop in different 'branches' and they are conflicted about which way to go. They might be afraid of losing their old self or making the wrong choice, and this internal struggle is what the angst in the fanfic is all about.
Mineta could react with a mixture of embarrassment and defiance. He's a proud character in his own way. So when All Might yells at him, he might try to put on a brave face and argue back a little. But deep down, he knows he's in the wrong. Eventually, he'll break down and start crying, realizing that he has disappointed not only All Might but also his classmates who are all striving to be heroes.
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.