One possible reason could be a curse. Maybe Naruto got caught in some ancient jutsu or curse that was meant for someone else. For example, a dark ninja from the past might have placed a curse on a certain bloodline, and Naruto accidentally triggered it because of his own unique chakra nature. Another reason could be some sort of experiment gone wrong. Orochimaru was always doing strange experiments, and perhaps he had a hand in this, trying to create a new form of power using Naruto as a test subject. It could also be related to a new power that Naruto is developing on his own. As he grows and faces new challenges, his body might be mutating in this strange way to adapt to a greater power he is about to unlock.
Maybe the horns are a sign of a new power awakening within Naruto. He could initially be afraid of them and hide them, but as he discovers their potential, he learns to embrace this new aspect of himself and use it to protect the village in ways he couldn't before.
One possible reason could be a sense of disillusionment. Maybe Naruto discovers some dark secrets within Konoha's leadership that make him question his loyalty. For example, if he finds out that some decisions were made that put the village at risk for the wrong reasons.
One possible reason could be extreme guilt. Maybe he fails to protect his friends in a major battle and feels so responsible that he can't bear it. For example, if Sasuke were to die because Naruto couldn't reach him in time, Naruto might sink into such deep guilt that he sees no way out but death.
Maybe he was poisoned. There are many villains in the Naruto world who use poison. If Naruto was poisoned during a fight or an ambush, it could lead to him coughing blood as his body tries to fight off the toxins. Just like how Sasuke was once poisoned and had to be treated.
One reason could be some sort of betrayal he feels. Maybe he discovers a secret that makes him think Team 7 was never truly his team. For example, if he found out that the village leaders had some ulterior motives for forming the team that involved using him.
Perhaps it's a training exercise that gets out of hand. In the world of Naruto, intense training often mimics real battles. If they were sparring and emotions ran high, it could turn into a full - fledged fight. Also, Sakura might be trying to prove herself to Naruto, and Naruto, not understanding her intentions, might respond aggressively.
One possible reason could be a hormonal imbalance. For example, if there was a problem with the thyroid gland and it started functioning differently, it might affect growth hormones. Another reason could be related to bone health. Maybe there was a discovery of a new treatment for a bone - density - related issue that had an unexpected side effect of promoting growth in adults.
One possible reason could be a genetic mutation. Sometimes, mutations in the genes that control growth can lead to abnormal and continuous growth. Another reason might be related to hormonal imbalances. If there is an overproduction of certain growth - promoting hormones, it could cause the cock to keep growing.
One possible plotline could be that Naruto discovers his new wings during a battle. Maybe he's in a really tough fight against a powerful enemy and suddenly, wings sprout from his back. This gives him an unexpected advantage in the air, allowing him to dodge attacks more easily and launch aerial assaults. Another could be that the wings are a result of some new chakra form he unlocks. He has to learn to control them, which could lead to some comical training scenes with his friends like Sasuke and Sakura trying to help him figure out how to fly.
One possible reason could be a mission gone wrong. Maybe Kakashi thought Naruto was too much of a liability during a particularly dangerous mission and, out of a sense of harsh pragmatism, decided to abandon him to ensure the success of the mission and the safety of others. However, this would be very out of character for Kakashi as he has always been protective of his students.