It could be that Naruto, with his empathetic nature, finds a way to reach into the very essence of the heartless. He might use his experiences of dealing with various enemies and his own inner struggles to form a connection. For example, he could use his Uzumaki bloodline powers in a unique way, like how he sometimes uses his chakra to influence others, but in a more profound way to control the heartless. Also, his ability to never give up and his strong belief in his friends and the village might give him the mental strength to take on this task of controlling the heartless.
Perhaps Naruto has learned some sort of ancient technique that allows him to control the heartless. This could be something he discovered during his travels or from an old sage. He may use a combination of hand signs and his own unique chakra signature to assert his control. And his status as a hero in the Naruto world gives him the confidence and the respect from others that could be used as a tool to help in controlling the heartless. He might also be able to draw on the power of the Nine - Tails in some way to achieve this control.
Well, in some fanfictions, Naruto might control the heartless through his strong will and the power of his chakra. Maybe he uses some new jutsu he developed specifically for this purpose.
One challenge could be that the heartless have a very different nature compared to the beings Naruto is used to dealing with. Their lack of emotions might make it difficult for him to find a way to connect and control them.
In fanfiction, it could be through his strong chakra control. Naruto has always had amazing control over his own chakra, and perhaps he can manipulate the 'heartless' by infusing his chakra into them in a certain way, influencing their actions or behaviors.
Another issue could be resistance from other forces. There might be some dark entities or villains who don't want Naruto to control the heartless. They could try to stop him, either by directly attacking him or by using their own powers to counteract his control methods.
Well, it could imply that the fanfiction about Naruto is lacking in emotional depth or empathy. Maybe it portrays the characters in a cold or unfeeling way, not in line with the original spirit of the Naruto series.
He becomes cold towards others. He no longer shows the warm smiles and friendly greetings that he used to. Instead, he might ignore people or give them cold stares.
A great 'Naruto Control Heartless' fanfic is 'Naruto: Heartless Redemption'. This story delves deep into Naruto's psyche as he tries to control his newfound heartless nature. It starts with Naruto experiencing a great loss that causes him to shut off his emotions. As the story progresses, he has to learn how to balance this new side of him with his true self. The fic also has some amazing fight scenes where Naruto uses his heartless state to his advantage, making for a really engaging read. It also explores the relationships he has with his friends and how they react to this change in him.
Perhaps a dark power corrupts him. In the fanfiction, there could be some sort of dark chakra or evil entity that latches onto Naruto. This entity could slowly eat away at his emotions, starting with his heart, making him gradually lose his ability to feel empathy and turn heartless.
In some fanfiction concepts, it could be due to a new, powerful jutsu he discovers or perhaps as a result of some ancient curse or blessing that is bestowed upon him.
In some fanfictions, Naruto might gain the ability to control iron through special training with a unique jutsu master. This master could teach him how to manipulate the iron elements in the environment using his chakra in a very specific way.
In some fanfictions, Naruto might gain the ability to control the weather through a special training. Maybe he discovers a hidden jutsu or power within himself during a difficult mission or in a secret place. For example, he could find an ancient scroll that teaches him weather - controlling techniques.