Snape might be initially shocked but then try to hide his concern. He's a complex character. He could act indifferent in public but secretly start to gather information about who is behind the abuse. He might also start to keep a closer eye on Harry without the boy realizing it.
Snape could be angry. After all, Hogwarts is supposed to be a safe place. He might immediately confront the abuser if it's a student, using his authority as a teacher. If it's a more powerful force, he'd use his intelligence and knowledge of dark arts to plan a way to stop the abuse. He may also feel a strange sense of protectiveness towards Harry, which he tries to suppress at first.
He'd probably be annoyed. Snape is a serious wizard and he might think fanfiction is a silly Muggle - influenced concept.
He'd probably be shocked. I mean, Dudley has always seen Harry as the odd one out in the family, and suddenly finding out he's famous in a whole different world of fanfiction would be quite a surprise.
Well, in many such fanfictions, Harry might be shocked at first. He probably feels a sense of pity for Draco too. After all, being under the Imperius Curse means Draco has no control over his actions.
Snape would likely be shocked and then enraged. Harry is supposed to be the hero of the wizarding world, and seeing him drunk would be a huge disappointment. He would most likely drag Harry to his office, lecture him about propriety and the expectations placed on him as a wizard, and probably assign some form of punishment like a long detention. But as he observes Harry more closely during this time, he might start to wonder what drove Harry to this and if there are deeper issues that need to be addressed.
Snape might initially be surprised. He could then use this knowledge in a rather Snape - like way, perhaps to gain an advantage in his complex relationship with Harry. Maybe he'd be a bit more guarded in his interactions with Harry, or he could even try to subtly help Harry overcome his fear while still maintaining his tough exterior.
He might be curious. Harry is always eager to learn new things. He'd probably read it with great interest to figure out what this new world of RWBY is all about.
Arthur might be shocked and immediately want to protect Harry. He could start by confronting those who are abusing Harry or find a safe place for Harry to stay.
Viktor might be shocked at first. He could feel a strong sense of protectiveness towards Harry. Maybe he immediately tries to comfort Harry and assure him that he's not alone anymore.
Well, Dumbledore has always had a special connection with Harry. When he finds out about the abuse, he would be devastated. His first instinct would be to comfort Harry. He might also reflect on his own actions and whether he could have prevented the abuse from happening. Dumbledore would then use all of his resources to make sure Harry is safe and happy. He could provide Harry with a mentor or a guide to help him through the difficult times, someone who can teach Harry how to cope with his past and move forward in a positive way.
Snape might be initially shocked. He has his own preconceived notions about Harry, and this revelation could completely change his view. He might struggle to accept it at first, given his traditional and somewhat rigid personality.