It's not a very common or popular concept. Harry Potter is typically seen as a hero opposed to Dementors, which are dark and terrifying creatures. Fanfiction usually focuses on more positive or heroic aspects of Harry's character rather than making him a fan of Dementors.
One common theme is fear. Dementors are known for instilling fear in people, and fanfics often explore how characters cope with this extreme fear. Another theme is the power of memories. Since Dementors feed on positive memories, many fanfics will revolve around characters protecting their memories or trying to regain lost ones. Also, redemption can be a theme, like when a character who has been affected by Dementors finds a way to turn their situation around and become stronger.
There might be a fanfiction where the Dementor Lord forms an alliance with Voldemort. Imagine the chaos they could cause together. The Dementors' ability to suck out souls combined with Voldemort's dark magic could create a truly terrifying scenario for Harry and his friends.
It would be really dark and mysterious. Harry as a Dementor Animagus would have some very different powers and abilities. He might be able to control the Dementors in a way, or use their fear - inducing abilities for his own purposes, perhaps in the fight against Voldemort. But it would also be a struggle for him to control his Dementor side, as Dementors are associated with negative emotions.
One interesting dementor - themed fanfiction could be 'The Dementor's Curse Reversed'. In this fic, a young witch discovers a way to turn the dementors' powers against them. It's a thrilling read as she battles the dark creatures in a new and unexpected way.
Well, it could be about a Harry Potter who has some special power over Dementors. Maybe he can control them instead of just fending them off with a Patronus. He could use this new - found power to his advantage in the wizarding world, like using Dementors to guard against dark wizards.
Another theme is the nature of darkness. Since Dementors are associated with darkness, fanfics often explore how the Dementor King embodies this darkness and how it affects the characters around him. They might look at how the characters struggle against this all - consuming darkness. For example, a character might have to find their inner light to resist the Dementor King's influence. It can also involve themes of redemption, as some stories may have the Dementor King or those influenced by him seeking redemption from their dark deeds. This adds a layer of complexity to the characters and the overall story.
One possible plot is that Harry absorbs the dementor in a moment of extreme danger. This changes him in some ways. His Patronus might become more powerful as a result. He may also start to understand the dementors' origin and find a way to stop their creation. He could then share this knowledge with the wizarding world.
Yes, it's possible in fanfiction. It could be justified as self - defense. If a dementor was about to attack an innocent, especially someone Harry cared about, he might be pushed to use a powerful spell to kill it rather than just the Patronus charm which usually just drives them away.
In a fanfiction where Harry Potter kills a dementor, it could lead to many consequences. First, the wizarding world might react with shock as dementors are usually just sent back to Azkaban. It could also change Harry's perception of himself as a wizard, as taking a life is a huge deal. Maybe he would face some sort of backlash from the Ministry of Magic for acting outside the normal procedures of dealing with dementors.