Perhaps after facing too much betrayal from the village he loves. If the villagers turned on him despite all his efforts to protect them, it might lead him to close his heart in self - defense, not wanting to be hurt again. He's always tried so hard to gain their acceptance and if that was all for naught, it would be a huge blow.
It could also be due to the constant pressure and expectations on him. He's always had to be the hero, the one to save the village. If he feels he's constantly failing or not living up to those expectations, he may close his heart to protect himself from that self - doubt and disappointment. In the fanfic, perhaps there are new threats to the village that he feels he can't handle, and this leads to him shutting down emotionally.
Well, it might start with Naruto distancing himself from his friends. He stops going on missions with them, and he doesn't show up at their usual gathering places. For instance, he might avoid Ichiraku Ramen, which was always a place of connection for him and his friends.
Self - reflection is key. If Naruto takes the time to really look at himself and understand why he closed his heart in the first place, he can start to work through those issues. Maybe he realizes that closing his heart is only causing him more pain in the long run and that by being open, he can experience the full range of human emotions again, both the good and the bad.
In fanfiction, it might be a result of a curse or some dark magic. For example, a villain could have cast a spell on him that weakened his heart both physically and emotionally.
It could be a misunderstanding as well. Raven Roth might misinterpret Naruto's actions or words. Let's say Naruto is trying to protect her in his own way but she takes it as him being overbearing or not trusting her. This misunderstanding could lead her to do something that breaks Naruto's heart, like distancing herself from him or saying hurtful things to him. In the world of fanfics, misunderstandings are often used as plot devices to create drama and emotional turmoil.
One possible reason could be that Naruto has seen the dark side of the shinobi world. He might have witnessed too much death and destruction in battles, and this has made him disillusioned. For example, if he lost many friends in a major war, he could start to question the whole concept of being a shinobi.
I recommend " Happiness on the Left " and " Contracted Boyfriend is the President " to you. " Happiness on the Left " was about a beautiful and cold girl who sealed her emotions in order to forget the pain of the past, until she met a man who closed his heart. " Contracted Boyfriend is the President " was about the male protagonist, Gu Han, who had learned to shut himself off due to the mysterious death of his parents. It was not until the appearance of the female protagonist, Xia Lewei, that his heart changed. Both novels described the protagonist's experience of emotional trauma and sealing off his emotions. I hope you like these recommendations!
Since it's a Naruto fanfiction, it might deal with themes of disillusionment. In the Naruto world, characters often face hardships and betrayals. The 'no longer in autumn' could symbolize a departure from a once - idyllic or nostalgic state. It could also touch on themes of self - discovery as the character's heart changes, perhaps realizing new aspects of themselves or their place in the Naruto world.
Another reason might be related to some sort of experiment gone wrong. Peter is often involved in scientific research. If there was an accident in his lab, perhaps with a new type of spider - related serum or some other experimental technology, it could have unforeseen consequences on his heart and lead to it stopping.
One possible reason could be to protect his friends. He might think that by sacrificing his heart, some great danger or enemy would be vanquished, thus ensuring the safety of those he cares about. For example, if there was a powerful curse that could only be broken by his heart's sacrifice.