In 'Harry Potter Controls Fiendfyre' fanfiction, how does Harry gain the ability to control Fiendfyre?

Well, it might be related to his connection with the Dark Lord. Since Voldemort was able to control the basilisk before, and Harry has a unique connection to Voldemort through the scar. This connection could be manipulated in some way in the fanfiction, allowing Harry to take over the control of the basilisk from Voldemort.

In some fanfictions, it could be through intense magical training and study. Maybe he discovers an ancient spell or a hidden magical technique that allows him to assert control over the dangerous Fiendfire.

One consequence could be that he is feared by others. Fiendfyre is a very dangerous and dark magic, so if Harry is seen controlling it, some people in the wizarding world might view him with suspicion and fear, thinking he is turning to the dark side. Another consequence might be that it drains his magical energy a great deal. Controlling such a powerful and volatile spell could take a toll on his magical reserves, leaving him weakened after using it.

Well, in some fanfictions, Harry might gain control over the Wizengamot through his heroic deeds. For example, if he saves the wizarding world from a great threat again, the public support could be so strong that he can influence the Wizengamot's decisions. He could also use his knowledge of magic, especially some ancient or powerful magic that gives him an edge in the political arena of the wizarding world.

It's possible that through his unique connection with Voldemort. Since they were so closely linked, and Voldemort was always obsessed with cheating death, Harry might have gained the ability to control death as a sort of counterbalance to Voldemort's attempts.

Maybe he discovers it during a particularly intense storm at Hogwarts. He could be in a dangerous situation, like being chased by some dark creatures, and in a moment of desperation, he unknowingly summons lightning to protect himself.

It could also be due to his own inner strength and growth as a wizard. Harry has faced so many challenges and traumas throughout his life. His experiences might have awakened a latent power within him that allows him to control dementors. His strong willpower and determination, which have been developed over years of fighting against the dark forces, could be the key factor in this newfound ability.

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 flood through a special training with a hermit who has water - based powers. This hermit could teach Naruto unique jutsu related to water manipulation on a large scale.

In some fanfictions, it could be related to an ancient bloodline limit that was dormant in Naruto all along. His Uzumaki heritage might have some connection to water - related powers, and through some sort of emotional or physical trigger, he is able to access and control the ocean.