Yes, there are some interesting 'Harry is a Dementor' fanfictions out there. Some explore the unique concept of Harry being a Dementor in a creative way, like how it changes his relationships with other characters. For example, his interactions with Hermione and Ron might become more complex as he now has this dark and somewhat feared nature.
Common themes include power and control. As a Dementor, Harry has certain powers that he needs to learn to control. There's also the theme of acceptance. How do the other characters in the wizarding world accept or reject Harry in his new form? And of course, the theme of the battle between good and evil within himself, as Dementors are typically associated with evil, but Harry has always been on the side of good.
It could be really interesting. Maybe Naruto somehow encounters Dementors in a strange crossover world. He might initially be confused by their ability to drain happiness but then use his ninja skills to fight back. For example, he could use his shadow clone jutsu to distract the Dementors while he figures out a way to deal with their soul - sucking power.
In this fanfiction, Dudley would surely interact with the Hogwarts professors. Professors like McGonagall would be strict with him, making sure he follows the rules. He might also cross paths with Draco Malfoy. Given Malfoy's attitude towards Muggle - borns, there could be some conflict there. And let's not forget the other students in his house. They would play a big role in his Hogwarts experience, either befriending or ostracizing him.
In the fanfiction, Ginny could be developed by exploring her magical abilities further in relation to Dudley. For example, she could use her magic to show Dudley the beauty of the wizarding world, which in turn makes her more confident in her own identity. Dudley's character can be developed by having him face his own insecurities. He realizes that Ginny is different from what he thought wizards were like, and this makes him question his own upbringing and beliefs.
In some Dudley Protects Harry fanfictions, Dudley's character development often starts with a significant event. For example, he might witness the true danger Harry is in from the wizarding world. This makes him realize that his previous bullying was petty. He then begins to feel a sense of responsibility towards Harry. He may start to learn about the wizarding world to better protect Harry, gradually changing from a bully to a protector. This transformation can also be influenced by his own growth in understanding family and loyalty, as he finally sees Harry as more than just the 'freak' he once thought him to be.
Well, perhaps Dudley uses his street - smart knowledge. He might teach Harry some rough - and - tumble moves he's learned from his own scuffles in the neighborhood. For example, showing Harry how to dodge a punch quickly.
Harry might become more open and less guarded. Since he now has a brother in Dudley, he might feel more at home in the Muggle world. Dudley, on the other hand, could become less of a bully. The knowledge that he has a wizard for a brother could make him more humble and empathetic.
One possible plot could be Hermione using her intelligence to find a way to repel Dementors without using a Patronus. Maybe she discovers some ancient magic or potion that can keep Dementors at bay. Another plot could involve a Dementor being somehow controlled by a dark wizard to specifically target Hermione, and she has to outwit both the Dementor and the wizard. There could also be a story where Hermione befriends a Dementor in a very strange turn of events, perhaps by understanding its true nature and finding a way to communicate with it, which would be a very unique take on the relationship between a character and a Dementor in fanfiction.
In a fanfic where Harry is kissed by a Dementor, he would likely lose his soul. This is because the Dementor's kiss sucks out a person's soul. It would be a very dark turn for the story. His friends would probably be devastated and the fight against Voldemort would take a huge hit as Harry was seen as a key figure in that battle.