What could be the possible reasons for Harry Potter throwing up blood in fanfic?

Perhaps he has been exposed to some sort of deadly and unknown substance in the mythical world. This could be a new type of monster venom or a strange plant that he accidentally ingested. The substance could be attacking his body from the inside, causing his internal organs to bleed, and thus he throws up blood.

It could be due to a dark curse or spell. Maybe he was attacked by a powerful dark wizard using a forbidden spell that affects his internal organs and causes bleeding.

Well, it could be a result of a dark spell cast on him by a Death Eater. Maybe they found a new and insidious way to harm him without leaving an obvious trace.

Well, it could be related to some sort of poison. Perhaps he was poisoned by an enemy who managed to slip something into his food or drink. The poison could be slowly corroding his insides and making him cough up blood as a symptom. It might also be part of a plot by a new villain in the fanfiction world who is trying to weaken Harry in a more insidious way than the usual dark wizards.

Maybe in the fanfic, there was a huge misunderstanding. For example, perhaps the Weasleys were wrongly accused of something that endangered Harry's life or the lives of his loved ones. It could also be that there was some sort of dark magic at play that made Harry believe the Weasleys were his enemies.

One possible reason could be a misinterpretation of his character. In the original series, Harry Potter doesn't hate Muggles at all. But in this fanfic, perhaps the author wants to explore a 'what if' scenario where something drastic has happened to make him have such feelings. Maybe he's been betrayed by a Muggle - in the fanfic world, this could be a made - up situation that sours his view on all Muggles.

It could be related to a new and strange power he's trying to control. Percy is constantly evolving and getting new powers. If he tries to tap into a power that his body isn't ready for, it might have some adverse physical effects like vomiting. Like when he first started to understand his water - based powers, there could be something similar but more extreme with a new power.

Perhaps in this fanfic, there has been some major plot twist that makes Harry believe that bowing to Voldemort is the only way to save his friends or the wizarding world. For example, Voldemort may have threatened to kill all of Harry's loved ones if he doesn't submit, and Harry is sacrificing his pride for the greater good.

Maybe he ate something bad in the fanfiction world. Like some enchanted food that didn't agree with him.

Well, it could be due to some sort of magical potion gone wrong. Maybe he drank something that was supposed to give him extra strength but instead made his stomach turn. Another reason could be that he got poisoned during a battle with a monster. Some monsters might have venom or toxins that could make him sick to his stomach.