A 'from the heart Naruto fanfiction' might also be about Naruto's relationship with his parents. It could be a story that reveals his mother's love for him through her chakra seal, and how his father's legacy influenced him. This can bring out a lot of emotions as it shows the family aspect that was somewhat lacking in Naruto's life for a long time.
You can start by looking on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just type in 'from the heart Naruto fanfiction' in their search bars and see what comes up.
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.
I don't think it's a common type. Most Naruto fanfictions tend to build on his existing character traits like his loyalty, his drive to protect his friends and village. A 'naruto has no heart' concept goes against the core of his character that fans usually love, so it's probably not a common genre in the Naruto fanfiction community.
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.
In some fanfictions, Naruto could break Hinata's heart by choosing another girl over her. For example, if he decides to be with Sakura instead. Hinata has always had deep feelings for Naruto, and seeing him with someone else would shatter her heart. It could also be that Naruto ignores Hinata's sacrifices for him and takes her for granted, which slowly breaks her heart as she realizes he doesn't value her as much as she thought.
Another possibility is Gaara before he met Naruto. He had a really tough childhood and was initially very cold - hearted, seeing others as tools or threats. His heart was like a frozen desert, until Naruto's friendship started to thaw it. In this fanfiction, they could explore more of his pre - Naruto state of a frozen heart and how it affected his relationships with others in the shinobi world.
For a 'naruto from the heart fanfic', you might consider writing about Naruto's experience with the Akatsuki. Not just the battles, but how it affected him on an emotional level. How did he feel when he faced Pain and saw the destruction of the village? What was going through his heart when he decided to forgive Nagato? These are deep emotional aspects that can be explored in the fanfic. You could also explore Naruto's heart - based growth as a leader. How his values and his big heart influenced his decisions when leading his team or the village.
Naruto might become more withdrawn. He's used to being this energetic and positive person, but after having his heart broken by Hinata, he could lose that spark. He might stop going out as much, avoid his friends, and just keep to himself.
One consequence could be that Hinata tries to move on but struggles a great deal. She might have a hard time opening up to anyone else in the future. Her self - confidence could also take a big hit. Since she put so much of herself into her feelings for Naruto, having her heart broken could make her question her own worth. Maybe she starts to think that if Naruto didn't love her, then no one will. This could lead to her being more reserved and less likely to take risks in relationships or in other aspects of her life.