There could be Peter's best friend. Maybe his friend has been encouraging Peter to stand up to Flash all this time. When Peter finally does it, his friend is right there by his side, supporting him.
In this fanfiction, Peter might stand up to Flash by using his intelligence. For example, if Flash tries to humiliate Peter in class, Peter could outwit him with his knowledge, showing that he's not someone to be pushed around. He could also gain the respect of his classmates in the process, which would be a big blow to Flash's ego.
Well, it could be about a scenario where Peter (presumably from some fictional universe) gets into a physical altercation with Flash. Maybe in this fanfiction, Peter has been pushed to his limits by Flash's actions or words, so he decides to beat him up. It could be a way for the author to explore the characters' relationships and emotions in a more extreme way.
Since Peter is Spider - Man, he has to be careful not to use his powers and reveal his identity. So he might just try to defend himself in a non - superhuman way, like using his quick reflexes to dodge Flash's blows as much as possible while trying to calm Flash down verbally.
One possible reason could be envy. Flash might be jealous of Peter's intelligence or popularity at school. Maybe he feels overshadowed by Peter and his achievements, so in the fanfiction, his anger and frustration lead him to lash out physically.
Obviously, Peter and Flash. It's possible that Peter is a hero - type character with a moral code that Flash has somehow violated. Flash could be a sidekick - turned - antagonist or just a regular character who has a conflict with Peter. Their personalities and the nature of their relationship in the original source material would be twisted in this fanfiction to lead to Peter beating up Flash.
Well, in this kind of fanfiction, it might show Bucky's loyalty to Tony. Maybe Tony is in some sort of trouble, and Bucky decides to support him. It could be related to the complex relationships within the Marvel universe. Bucky, with his own set of values and experiences, steps in for Tony, which can lead to interesting character developments and interactions.
One possible scenario in such a fanfiction could be a school - related incident. Flash taunts Peter in front of everyone, and Peter, tired of it, decides to fight back in a more subtle way. Maybe he uses his super speed and reflexes to dodge Flash's attacks and make Flash look foolish without using full - on Spider - Man powers.
One key moment could be in the potions class. Snape might be unfairly criticizing Hermione's potion - making skills, and she just refuses to take it silently and stands up to him, stating her case clearly. Another moment might be when Snape is being overly harsh on one of her friends, and Hermione steps in, protecting her friend and facing Snape's wrath head - on.
One possible fanfiction could be where Jon Snow stands up to the Night King directly. He might use his skills and knowledge of the enemy to taunt the Night King, saying that he will never succeed in his dark plans. This shows his courage and determination to protect the realm.