It could be due to a blood - magic related incident. Suppose there is some long - lost connection between Harry's family and the origin of Dementors. A spell or a ritual that awakens this connection might endow Harry with Dementor - like powers. For example, if there was an ancestor who was involved in the creation of Dementors in some way, and that knowledge or power was passed down in a latent form in Harry's blood.
Well, in some fanfictions, dementor powers are extended to include mind - control over a larger scale. They might be able to not only suck out happy memories but also implant false ones. This could create really complex and dark storylines where characters are manipulated in more insidious ways.
He might be feared by others. Since Dementors are known for their terrifying and soul - sucking abilities, people would be very cautious around Harry. His friends might even be initially scared of him until they understand he can control these powers.
Some writers make dementor powers more psychological. Instead of just sucking out happy memories physically, they can make it so that the dementors can influence a person's thoughts and make them doubt their own happy memories, as if the memories are being corrupted from within.
It could also have the power of dark concealment. Dementors are known for their ability to blend into the darkness and appear unexpectedly. Their blood might be used in spells or charms that allow a wizard or witch to move undetected in the shadows, similar to how Dementors move. However, this power would likely come with a cost, as using dark - based substances often has negative consequences in the wizarding world.
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.
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.