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 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 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.
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.
One reason could be overusing his chakra. In Naruto's world, chakra is like life energy. If he overexerts himself and drains too much chakra, it can cause internal damage, leading to coughing up blood. For example, when he was training intensively or during a tough battle where he pushed his limits.
It could be a sign of a major turning point. If Naruto starts coughing up blood, it might signal that he's in a really dangerous situation and needs to find a way to get out of it fast. This can lead to new adventures as he searches for a cure or a way to regain his strength.
Physically, he might gain new powers or abilities as mentioned before. But there could also be negative effects. His body could reject the foreign blood, leading to internal pain and weakness.
It could be the result of Naruto's own inner demons. Maybe he discovers some dark secret about his past, like his parents being involved in something he can't accept. This self - realization could be so traumatic that it makes him cry blood as he struggles to come to terms with it.