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.
One possibility could be that Naruto is betrayed by someone he deeply trusts, like a close friend turning on him due to some misunderstanding or being influenced by an enemy. This betrayal cuts so deep that it makes him cry blood, perhaps in a moment of extreme emotional pain and shock.
Sakura could be the one to find him crying. She has known Naruto for a long time and they are comrades. If Naruto is in a vulnerable state, she might stumble upon him.
It can also be a turning point in Naruto's character development. If he's crying blood, it means he's likely facing a situation that challenges him in a way he's never been challenged before. This could lead to him growing stronger, either physically or mentally. He might gain new powers or a deeper understanding of himself and his abilities as a result of this traumatic experience.
One possible reason could be that Naruto is feeling lonely. Despite having friends, there are times when his past as an orphan and the years of being shunned by the villagers resurfaces, making him feel isolated. Kakashi finding him in such a state might then lead to a heart - to - heart conversation about Naruto's inner struggles.
One possible reason could be that Naruto is feeling lonely. Despite having friends, he still has moments when the weight of his past, like being an orphan and ostracized in the village as a child, hits him hard. Jiraiya might see Naruto crying because of these memories resurfacing.
One reason could be the loss of a fellow shinobi. In the Naruto universe, comradeship is highly valued, and if Kotetsu were to lose someone close to him in battle or otherwise, it would be a very emotional moment that could lead to crying.
One possible reason could be the loss of a dear friend. Naruto forms deep bonds with his comrades, and if something were to happen to them, like Sasuke leaving again, it would break his heart and make him cry.
Perhaps in this fanfiction, Naruto is in a situation where he has no other source of sustenance. He could be trapped in a desolate place with no food or water, and the blood becomes a last - resort option for survival. This would be a very dark and extreme take on the character, as it goes against his usual values.
Betrayal is also a theme. If Naruto is betrayed by someone he trusts, it can lead to a very emotional response. His crying in such fanfictions is a way to show the depth of his hurt and how difficult it is for him to process that kind of pain.
One possible fanfiction could be that Kakashi stumbles upon Naruto crying alone in the forest. He sits beside Naruto quietly, not saying a word at first. Then he gently puts his hand on Naruto's shoulder and tells him that it's okay to cry, that showing vulnerability doesn't make him weak. Naruto then pours out his heart about his loneliness and how much he misses his parents. Kakashi listens intently and shares some of his own experiences of loss, creating a deep bond between them in that moment.