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.
His character might become more complex. He could have a darker side that he has to struggle with. For example, he may be more withdrawn at times due to the dementor's influence.
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.
I don't think it's common. In the Harry Potter fandom, we often discuss things like the latest fanfiction trends, which characters are popular in fanfiction, or how fanfiction fills in the gaps in the original story. Statements about Harry Potter 'absorbing' fanfiction are not typical. Most people see fanfiction as a separate, creative outlet for fans, not something that the main Harry Potter entity 'absorbs'.
I'm not sure if there's a particular well - known fanfiction with exactly this plot. There are so many fanfictions out there that it's hard to keep track. You might have to do some in - depth searching on fanfiction websites.
In some fanfictions, Harry Potter might absorb abilities through magical artifacts. For example, he could find a special amulet that transfers the powers of the previous owners to him when he touches it.
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.