Perhaps a group of friends who are all fans of Harry Potter. They could be sitting around one day, joking about different scenarios, and then one of them decides to write it down as a fanfiction. They might share it among themselves for a good laugh and then it somehow makes its way out to a wider audience.
Perhaps it's part of a wild adventure. Harry could be exploring a mysterious place and accidentally falls into a pool of water in a very awkward position, making it seem like his butt got filled with water. This could lead to a series of events where he has to figure out how to dry off and deal with the embarrassment.
One main theme could be transformation. When Harry is filled with water, it might symbolize a change in his character or abilities. For example, he could become more fluid in his thinking or more adaptable, just like water.
One popular 'Harry filled with water' fanfiction might be 'The Watery Adventure of Harry'. It's a story where Harry gets caught in a magical rainstorm that floods the Hogwarts grounds and he has to use his magic in unique ways to deal with the situation.
Aspiring young writers who are fans of the magical world. They see Dumbledore as a rich character to base their fanfiction on. They could be students who are inspired by the detailed world of Hogwarts and want to contribute their own ideas about Dumbledore through writing.
Hermione might help Harry. She's always good at giving advice on how to handle social situations. She could tell Harry exactly what to say to Parvati to make his apology sincere and effective.
There's a chance that some unexpected characters could have helped. Maybe Luna Lovegood, with her unique perspective on magic and the wizarding world. She might have known some ancient spells or secrets that were useful. And Neville Longbottom, who had grown into a strong and capable wizard. He could have provided a distraction or used his skills in Herbology to create something that was essential for the faked death to be convincing, like a plant that mimicked the symptoms of death.
In GOT (Game of Thrones) fanfiction, Harry Peverell is likely a character created by the fanfic writer. He could be an original character inserted into the complex world of Westeros, perhaps with a unique backstory, abilities or a role to play in the events that the fanfic author has crafted. However, without specific details about the particular fanfiction in question, it's hard to say exactly who he is.
His friends would surely be affected. Hermione and Ron might be both amazed and a bit worried. They could be worried that this new power might change Harry too much or put him in more danger. Also, his enemies like Draco Malfoy would be affected. Draco might become more jealous or even more afraid of Harry.
It could be Death Eaters. They might have finally found a way to capture Harry without alerting Dumbledore. His 16th birthday could be the perfect opportunity as everyone might be a bit more relaxed thinking he's not quite of age yet for the full - on final battle.
Hermione would be a likely helper. She's smart and practical, and she could help Harry figure out what to do with all the stuff in the vaults, like how to properly inventory and distribute the items.