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.
Maybe it's a rogue group of wizards who fear Harry's power over Dementors. They might think that Harry is going to use the Dementors to take over the wizarding world in an unjust way. So they band together to try and stop Harry before he can fully embrace his role as the King of Dementors.
One great 'Harry Potter Dementor King Fanfiction' could be 'The Dementor's Reign'. It explores a world where the Dementor King has a more prominent role in the wizarding world. It's full of interesting plot twists and new takes on the magical lore of Harry Potter.
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.
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 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.
One interesting plot could be a new character with a special power to repel Dementors. This character might be an outcast in the wizarding world at first but then becomes crucial in a major Dementor attack on Hogwarts. They could use their power in a unique way, like creating a shield of positive memories that not only protects themselves but also those around them.