It could also be a new power he discovers. In many fanfictions, the author gives Naruto unique abilities that are not part of the original story. So, this could be a power that is specifically designed to deal with the heartless. Maybe it has something to do with his connection to the nine - tailed fox. The fox's power might be modified or used in a new way to control these heartless entities.
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.
Well, it might be related to his ability to understand and empathize with others. Naruto has a big heart and can often see the good in people. Maybe in this fanfiction, he uses this empathetic side to connect with the heartless on some level, and then gain control over them. He could be reaching out to whatever small bit of 'heart' or consciousness they might still have.
Chapter 442, "Dropping Them At Their Destination", is the clearest early answer because it turns Damien's situation into a concrete plot event. The chapter gives readers a real answer by opening on The morning began quietly—too quietly for Damien's liking. and ending on The slime had appeared quietly from Damien's blue summoning portal.... In story terms, the chapter closes with "I let them play me," he muttered.
Chapter 495, "You'll Make It Back In Time", is the clearest early answer because it turns Garrick's situation into a concrete plot event. The setup is A low, vibrating bellow rolled through the trees., but the pressure keeps building through Garrick's hand went to his weapon instantly..
Chapter 229, "Another Mission Already", is the clearest early answer because it turns Damien's situation into a concrete plot event. It opens with Damien and Arielle walked through the bustling streets of Westmont,... and closes on After several minutes of walking, he came upon a clearing..
Chapter 262, "Delayed Travel", is the clearest early answer because it pushes Damien into a new phase or setting. The setup is The Teleportation Center described to Damien loomed before him, a..., but the pressure keeps building through Unlike the bustling streets and crowded taverns, this place exuded an....
Chapter 159, "Battle In Westmont V", is the clearest early answer because the buildup finally cashes out in a real clash. The setup is The battle was a maelstrom of chaos., but the pressure keeps building through Smoke, dust, and the acrid stench of burning buildings filled the air..
Chapter 321, "A Send Off Party", is the clearest early answer because it turns Damien's situation into a concrete plot event. Early on, The sun had already dipped behind Westmont's tallest rooftops when a.... By the end, You kept it small." "As requested.. Inside the broader power growth storyline, the chapter closes with At dawn, they would leave Westmont behind., which gives this chapter's turning point a stronger narrative position and pushes the relationship tension onward.
Chapter 268, "Assembling A Team Of Four", is the clearest early answer because it turns Damien's situation into a concrete plot event. The setup is Damien emerged from the teleportation array, blinking against the..., but the pressure keeps building through Unlike Velhast's cold morning air, Ryedale was warmer, a sign that....
Chapter 271, "People From His Homeland", is the clearest early answer because it turns Damien's situation into a concrete plot event. It opens with Damien sat in his room, staring blankly at the wall, his mind still... and closes on I assume you're here to ask about the visitors from yesterday.".... The key payoff is that the chapter closes with Damien's expression darkened slightly., which gives power growth a stronger narrative position and pushes the power growth onward.
Chapter 285, "Lost Battle I", is the clearest early answer because the buildup finally cashes out in a real clash. The setup is With one powerful dive, the wyvern swooped down, claws extended., but the pressure keeps building through A group of mercenaries screamed, trying to flee but they weren't fast....
Chapter 32, "Attack of the Cold Beast", is the clearest early answer because the buildup finally cashes out in a real clash. The chapter turns that into something concrete by moving from The small fire pit, after upgrading to an iron refining furnace, has... to Even though upgrading to an iron refining furnace doubles the daily....