In some versions of the fanfiction, it could be due to his unique heritage. Since Harry has a complex family background in the wizarding world, there might be some long - forgotten blood magic in his lineage that surfaces unexpectedly. One day, during a duel where he gets a minor cut and his own blood is exposed, he notices that he can somehow manipulate the flow of blood, and that's how he discovers this ability.
In fanfiction, the possibilities are endless. Regarding Percy controlling blood, it could be part of a larger, more complex power set. For example, it could be related to his connection with a certain element or magic. Maybe it's a result of a curse or a newfound ability after a life - changing event. This power of blood control can be used in various ways in the story, like for healing (by manipulating the blood's properties), or for more sinister purposes such as coercion or combat. Fanfic writers use such concepts to add depth and novelty to the familiar character of Percy.
He might also face moral dilemmas. For instance, using this power to heal someone might seem noble, but if he uses it to harm or manipulate others, it would be a different story. He has to constantly struggle with the right way to use this power.
Another feature is the character development centered around the blood control ability. Characters may struggle with the morality of using such a powerful and somewhat gory ability. They might have to overcome their own fears or the prejudice of others. In some fanfictions, characters with blood control abilities are ostracized at first because it's seen as something unnatural. So, it makes for really interesting internal and external conflicts.
One popular 'naruto blood control fanfiction' is 'Bloodline's Legacy'. It delves deep into a unique take on blood control abilities in the Naruto universe. The story follows a new character who discovers an ancient bloodline related to blood control and how it changes his journey in the ninja world.
Well, in such a fanfiction, he might control space through his magic wand. Maybe he uses a special spell that he discovers or invents, which allows him to manipulate the fabric of space, like creating portals or warping distances.
One consequence could be that the wizarding world starts to view him with even more suspicion and fear. People are already afraid of dementors, and if Harry can control them, they might think he's becoming too powerful or even turning to the dark side.
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.
It could be through some kind of inheritance. Perhaps he has some long - lost family connection that gives him this unique power. In the fanfiction, he might start noticing strange things happening around cold or icy elements, and then gradually realize that he can actually control them.
Perhaps it is related to some old magic that he inherits. One day, when he is exploring an old, abandoned place like an ancient wizard's tower. There, he touches an old relic which activates this hidden ability. As soon as he touches it, he feels a strange connection with the shadows around him and realizes he can control them.