Some bullies might mock BTS fanfic. They could make fun of the fans who write or read it, thinking it's just some silly obsession. They might not understand the creativity and passion that goes into creating these fanfics.
Some bullies might mock or make fun of spiderman fanfic. They could see it as something only 'nerds' are into and use it as another reason to pick on fans. For example, they might laugh at the outlandish plot ideas or the 'geeky' passion of the fans.
Izuku would probably be terrified at first. After all, he's been kidnapped by villains. But then, his hero - like determination would kick in. He might start looking for ways to escape or at least resist their plans.
They're popular because they play on the idea of the members of BTS being in a difficult situation. Fans like to see how their idols would react to something like being wrongly accused of bullying. It gives a chance to explore different sides of their personalities.
One popular 'BTS Bullies React' fanfic might be 'The Change'. In this fanfic, the members of BTS react to a situation where they are wrongly perceived as bullies. It has an interesting plot that shows their shock and determination to clear their names. Another could be 'BTS Bullies React: The Hidden Truth' which delves into a mystery surrounding false accusations of bullying against them. It keeps you on the edge of your seat with its twists and turns.
Percy could react by ignoring Clarisse at first. He might think that if he doesn't give her a reaction, she will stop. But when that doesn't work, he could start to fight back verbally, using his quick thinking to come up with comebacks.
All Might would be furious. He would see it as his failure to protect Izuku. He would probably mobilize all the resources he has, both in his hero form and his connections in the hero world, to rescue Izuku. And he would be blaming himself all the while for not being there when Izuku was kidnapped.
Some characters might be immediately terrified. They could avoid Izuku or even try to drive him away. For example, classmates who don't understand his quirk might spread rumors about him.
Obviously, he would interact with his younger self. His younger self is a key character as Izuku from the future tries to guide and influence him. Also, All Might is likely to be an important character he interacts with. All Might has a huge influence on Izuku in the original story, and in the past, Izuku could have a different kind of interaction with him, perhaps sharing future knowledge about threats to hero society. His mother would also be someone he interacts with, as she is an important part of his life.