One possibility in this fanfiction is that Naruto is exposed to a powerful and otherworldly energy source. This energy could be from a different dimension or a long - forgotten relic. When he comes into contact with it, his body absorbs and adapts to it in a way that allows him to control black fire. This new power also comes with its own set of challenges and responsibilities for Naruto as he tries to integrate it into his existing set of skills.
It could be from some sort of ancient ninja training that was lost and he somehow discovers it. Maybe there's a hidden scroll or a hermit who teaches him this fire - controlling ability.
In some fanfictions, it could be through a moment of extreme danger or intense emotion. For example, he might be in a situation where his friends are in peril from a fire - based threat. His strong desire to protect them could trigger this hidden ability. It's like a latent power that surfaces when his will is at its strongest.
In this type of fanfiction, Bella might be in a world where different elemental powers are at war. Her fire - controlling ability is crucial in the fight against those who control water or ice. She has to find a way to combine her power with others who have different abilities to defeat a common enemy.
If Naruto can control fire in the fanfiction, his combat style might change significantly. He could combine his fire - controlling ability with his shadow clone jutsu. For example, his clones could all launch fire attacks simultaneously, overwhelming his enemies. Also, he could use fire to enhance his physical attacks, like coating his fists in flames for more powerful punches.
A possible storyline is that Naruto is transported to a parallel dimension where all ninjas have elemental powers from birth. There, he is initially at a disadvantage because he doesn't know how to use his new - found fire control. But with the help of some friendly locals, he starts to master it and eventually uses it to fight against an evil dictator in that dimension who is trying to take over all the ninja clans. Another storyline could be that Naruto's fire control is tied to his emotions. So, when he gets angry, the fire becomes uncontrollable. He has to learn emotional control along with mastering the power to use it effectively in battle and in his daily ninja life.
He could control elements like water, which would allow him to create powerful waterfalls or form water - based defenses. Fire is also a possibility, enabling him to shoot out intense flames. Another type could be earth, where he can manipulate the ground to create barriers or traps.
Bella's ability to control fire could be part of a coming - of - age story in fanfiction. She initially struggles with her power, afraid that she might hurt those she loves. As the story progresses, she meets a mentor who helps her understand and master her fire - controlling skills. This newfound confidence allows her to stand up to bullies in her school and also helps her in other aspects of her life, like making new friends who are drawn to her unique ability.
In some fanfictions, it could be due to a new jutsu he discovers. Maybe during a secret training session in an ancient scroll, he finds a forbidden technique that allows him to control people.
Well, in some fanfictions, Naruto might gain the ability to control nature through intense training with a hermit or some ancient spirit. For example, he could be led to a hidden grove where the essence of nature is concentrated, and by communing with it over time, he gradually unlocks the power to control nature.