One possible reason could be the loss of his friends. Naruto values his friends deeply, and if he were to lose someone like Sasuke again, it would be devastating. Another reason might be the pressure of being the Hokage. The responsibilities are huge, and he might feel like he's not living up to the expectations of the village. Also, memories of his lonely childhood could resurface, making him feel sad and alone, leading to him crying himself to sleep.
Perhaps it's related to the discovery of some dark secrets in the village. Naruto is very loyal to Konoha, but if he were to find out some unethical or cruel things that the village leaders had done in the past, it would shatter his idealized view of the place. This internal conflict and disappointment could lead to him crying himself to sleep as he tries to come to terms with it.
One possible reason could be the stress of his ninja duties. He has so many missions and responsibilities that his mind is constantly racing, making it hard to relax and fall asleep.
One possible reason could be that he is lonely. In many fanfictions, Naruto is often ostracized as a baby due to the Nine - Tails inside him. He might be crying because he feels the lack of a warm, loving presence around him.
Love. Just like any other character, Draco can be heartbroken in fanfiction. If he loses someone he loves, whether it's a friend or a romantic partner, he could cry. It shows his vulnerability and that he's not just the tough - guy Slytherin he often tries to be.
Isolation. Snape is a lonely character. He doesn't have many friends, and he is constantly in a difficult position between the Death Eaters and the Order of the Phoenix. His feeling of being alone and not being fully understood by anyone can lead to crying in fanfiction.
She might be crying out of frustration. For example, if she's been trying really hard to achieve a certain goal in the fanfiction, like mastering a new jutsu in a Naruto - themed fanfiction, but keeps failing. The stress and disappointment could lead to tears.
Another reason might be that he feels a great sense of guilt. For example, if he made a big mistake that had serious consequences for others, he would be overcome with guilt, which could manifest as crying.
Perhaps he feels a sense of loneliness. Even though he has the Lost Boys, there might be times when he realizes that he is different from them. He is the only one who truly doesn't age, and this realization could hit him hard and cause him to cry, as shown in some fanfictions.
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.
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.
Perhaps Naruto has just learned some dark secrets about his past, such as the truth about his parents' death. Discovering such painful truths could easily make him break down and seek comfort in Kakashi, who he looks up to as a mentor. Also, it could be that he's feeling lonely. Despite having friends, there are times when the weight of his responsibilities makes him feel isolated, and crying in Kakashi's arms is a way to let out those pent - up emotions.