He may see it as an opportunity. Maybe he'll think that he can now focus more on his training or on helping to protect the world without the restrictions of school. He could start to explore his Saiyan powers more freely and look for ways to use them for good outside of the school environment.
He might be angry at first. After all, he may feel that the school doesn't understand him or his situation. He could be thinking that his actions were justified in some way.
Trunks could also be a bit sad. He might have friends at school that he'll miss. And he may realize that being expelled is going to make things difficult for him in the future, like getting into another school or having a normal life among humans.
One possible reason could be getting into too many fights. If Trunks is constantly using his Saiyan strength to defend himself or others in a violent way, the school might expel him. Another reason could be skipping classes. Maybe he's off on some adventure or training instead of attending school.
Jaune could also become angry and frustrated. He might feel that the system is unfair and that he's being wrongly punished. So he could lash out at those he believes are responsible for his expulsion, whether it's a fellow student who set him up or a teacher who didn't give him a fair hearing. In some cases, he may even try to expose the wrongdoings or secrets of the school as revenge for his expulsion.
Well, he might be really flustered. Percy is often portrayed as a bit of a goof in some fanfictions. He could stutter and turn red, not really knowing how to handle the situation.
He might be extremely angry and feel a great sense of injustice. He has always seen Hogwarts as his true home, and being expelled would be like losing his family. So he would probably fight back, trying to prove his innocence and get his expulsion reversed.
He could also react with confusion. Natsu is a bit of a simple - minded character in some ways, and he might not understand why someone would want to bully him. This confusion could lead to him trying to figure out the bully's motives.
He might be really angry at first. Natsu is a passionate character, and being kicked out unjustly would make him furious. He could storm off vowing to prove his worth and show the guild they made a mistake.
He might be initially in shock. Percy has been through a lot with Annabeth, so being dumped would come as a huge blow. He could be speechless for a while, unable to process what has just happened.
He might be shocked at first. Naruto is used to seeing Kurenai as an ally, so being hurt by her would be unexpected. He could immediately ask her why she did it. If it was a serious injury, he might struggle to stay conscious while trying to understand the situation.
At first, he's likely to be shocked. Issei is often portrayed as a character who trusts easily, so betrayal would come as a big surprise. He might not believe it at first and try to find reasons to justify the actions of the person who betrayed him.
Well, Sirius could get really flustered. It could lead to some comical or tense moments depending on the context of the fanfiction. The howler might reveal something he doesn't want others to know.