It's also possible that there are some students who are under the influence of dark magic or dark wizards outside of Hogwarts. These students could be bullied into bullying Harry. Maybe they are threatened that if they don't make Harry's life miserable, something bad will happen to them or their families. So they become the tools of the real villains behind the scenes to bully Harry at Hogwarts.
Sometimes, it might not be just Slytherins. There could be some older Gryffindor students who feel that Harry is getting too much attention. They might pick on him to assert their own status within the house. Or, there could be students from other houses too, who for some reason, like some sort of misplaced rivalry or just plain nastiness, target Harry. For example, a Ravenclaw who thinks Harry is getting special treatment in classes and decides to bully him to 'put him in his place'.
In fanfiction, it could be some of the Slytherin students. They might be jealous of Harry's fame as 'The Boy Who Lived' or his friendship with popular Gryffindors. Malfoy and his cronies are often depicted as bullies in the original series, so they are likely candidates in the fanfiction as well.
Another way Harry could deal with it is by getting the support of the Hogwarts faculty. He could gather evidence of the bullying, like spells cast at him without provocation or mean - spirited remarks. Then, he could present this evidence to a trusted teacher, such as Professor McGonagall. She would likely take action against the bullies, perhaps giving them detention or restricting their privileges. This would not only stop the bullying but also show that there are consequences for such actions at Hogwarts.
Well, it could be some students who are part of a clique that doesn't like Velvet's quiet and introverted nature. They might see her as an easy target. Another possibility is that there could be some characters who have a grudge against Velvet for some past incident that we don't know about yet in the fanfictions. Also, there might be bullies who are just following the crowd and think it's cool to pick on Velvet.
Obviously, Harry Potter himself would be the main character. Hermione and Ron would also be important as they are Harry's closest friends and would be involved in his journey as the heir.
He could confide in his friends like Ron and Hermione. They would surely support him and come up with a plan to stop the bullying.
Ron would be there too. He could be in charge of things like the Gryffindor common room or helping Harry with student relations. And of course, Dumbledore might still have some influence in the background, even if Harry is in control. His wisdom could be a guiding force for Harry as he navigates running the school.
Neville Longbottom could be a key character. He might take on a bigger role in Hogwarts in Harry's absence and also be in touch with Harry, providing support from the school. Ginny Weasley would also be involved as she has a close relationship with Harry. Additionally, some of the Hogwarts professors like Professor McGonagall could play important parts, either trying to bring Harry back or helping him in his mission outside the school.
One reason could be jealousy. Harry is famous in the wizarding world, and some students might be envious of that. So they bully him to make themselves feel better.
Yes, in some fanfictions Harry Potter is bullied at Hogwarts. In these stories, it might be by the Slytherins who are often portrayed as the antagonists. They could use magic in mean ways against him, like jinxing his books so they won't open during class or tripping him with magic in the hallways.
It could be Draco Malfoy. In the original series, he often bullied Harry, so it's likely he would be the main bully in this fanfic as well.
Some of the likely characters could be the regular mortal kids at Percy's school. They might not understand his differences and bully him because of his ADHD and dyslexia. Another possibility is some jealous demigods who envy Percy's popularity or his special abilities.