His friends might be in it too. They could be the ones who join Harry on his yacht trips, having fun together. Maybe there's a character who is a bit of a troublemaker among his friends, always getting into funny situations on the yacht.
Maybe it's about Harry's luxurious adventures on his yacht. He could be sailing to exotic islands, hosting parties on the yacht with his friends.
Dumbledore could be a character in the fanfiction. Maybe he knew about the island all along and left it to Harry in his will. Or he could be a guiding spirit for Harry as he figures out what to do with the island.
Obviously, Harry is one of the main characters since he owns the cafe. There might also be his employees, like a barista who is really good at making coffee and has a great personality.
I don't know who the author of that fanfic is. There are so many fanfic writers out there and without more information it's hard to tell.
The writer may face a lot of criticism from the fan community. Most fans of the source material (presumably related to Harry) would not want to see such a dark and immoral concept associated with their beloved character. It can also damage the writer's reputation within the fanfiction writing community.
One plotline could be Harry renovating Hogwarts. He might discover hidden rooms or passages and use his newfound power to make the school safer or more inclusive for all students.
Well, Sirius Black is quite popular in harry possible fanfic. His relationship with Harry as a sort of father figure can be further explored. Luna Lovegood is another one. Her unique perspective on the wizarding world can be expanded upon in fanfics. And then there's Ron Weasley. Fanfic writers often play with his character, his loyalty to Harry, and his growth as a wizard.
His professors could also be in it. Professor Dumbledore might make an appearance and give Harry some wise Christmas advice. And Professor McGonagall could be there to ensure that all the Christmas celebrations are in line with Hogwarts' rules. Also, there could be some new characters, like a mysterious wizard who arrives at Hogwarts during Christmas and has some connection to Harry Greengrass.
Often, the main characters in yacht top stories are the wealthy owners. These are people like billionaires, movie stars, and oil tycoons who can afford these extravagant vessels. They are the ones who commission the building of these yachts and are at the center of the luxury and glamour associated with them.
There could be Firenze, the centaur. Centaurs are known for their wisdom about the forest and its creatures. He might be able to guide Harry to the unicorn and provide some herbal remedies or magical advice for the healing process. Also, Hermione could be involved. She would surely do a lot of research in the library to find the best way to heal the unicorn.