It could be a new dark wizard. There are always new threats emerging in the fanfiction world. This new dark wizard might have a vendetta against Harry and uses a special spell or potion to make him cough up blood.
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.
Well, it could lead to a lot of self - discovery for Percy. He might start to question his own mortality and his role in the story. This could make him more determined to fight against whatever is causing his condition. His relationships with other characters could also change. Some might become more protective, while others might be afraid to get too close in case they catch whatever is wrong with him.
One reason could be overexertion of his chakra. In many fanfictions, Naruto might push his chakra limits while using a powerful new jutsu he's created or trying to master. This overextension can cause internal damage, leading to coughing up blood as his body struggles to cope. Another possibility is that he's been poisoned. Some fanfic writers might introduce a new villain who uses a slow - acting poison on Naruto, which gradually weakens him and causes such symptoms.
It can make him more determined. When Naruto coughs up blood in fanfiction, it often shows that he's facing a serious threat. This could fuel his determination to overcome whatever is causing it, whether it's a new enemy or a personal ailment. He'll be even more driven to prove himself and protect those he cares about.
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.
Since I'm not familiar with specific 'amy coughs' fanfic, it's hard to say. But generally in fanfic, common themes could be relationships, personal growth, or challenges faced by the characters. Maybe in 'amy coughs' fanfic, if 'amy' is a character, it could be about her dealing with an illness (the cough) and how it affects her relationships or her journey.
There may or may not be a fanfic about Amy Fleming's coughs. It would depend on the creativity of the fanfic writers. Some might find the idea of focusing on such a detail as her coughs to be an interesting way to add depth to her character or to create a unique plot line within the fanfic world. But without extensive research in the fanfic communities dedicated to the relevant work that Amy Fleming is from, it's hard to say for sure.
I'm not sure specifically which 'amy coughs' fanfic is popular. You could try searching on fanfic platforms like Archive of Our Own (AO3). They have a vast collection of fanfictions, and you might be able to find relevant ones by using the search term 'amy coughs'.