Obviously, Harry Potter himself would be a central character. His friends like Hermione and Ron would most likely be there too. They could play a role in helping Harry understand and control his power, or they might be in danger and Harry's unleashed power is what saves them.
There could also be some new characters introduced. Maybe a mysterious old wizard who knows the secrets behind Harry's power and guides him. Or an antagonist, perhaps a Death Eater who is after Harry because of his newly discovered power, seeing it as a threat to their dark plans.
The Hogwarts professors, such as Dumbledore (even if it's in a spiritual form) or McGonagall, might also be important characters. Dumbledore could have left some clues about Harry's power before his death, and McGonagall could be there to support Harry and the school when his power starts to cause some commotion or attract unwanted attention.
Perhaps the fanfic focuses on Harry's emotional journey as he unleashes his power. He could start off being afraid of this newfound strength, but then learns to embrace it. He might face some internal struggles, like whether using his power is the right thing to do, especially if it has some unforeseen consequences.
In this fanfic, Harry is the main character. However, we could also expect to see Dumbledore making an appearance. Dumbledore has always been a guiding figure for Harry, and in a story about Harry showing his power, Dumbledore might offer some wisdom or crucial information. Neville could also be a key character. He has his own growth in the original series, and in this fanfic, he could be inspired by Harry's power and contribute to the overall plot in some way.
Obviously, Harry Potter is the main character as it's about him hiding his power. His friends, like Hermione Granger and Ron Weasley, are also likely to be main characters. They might be in the dark about his hidden power at first, which could create some interesting dynamics in their relationships.
It's hard to say without reading it, but it could be Harry, Hermione, and Ron. Since it's a Harry Potter fanfic, they are often the main characters in many fan - made stories. They might be the ones to discover the stones and their power.
Hermione and Ron might also be main characters. They are Harry's closest friends in the original series, and in a fanfic, they could play important roles in exploring the power within, maybe by using their knowledge and skills to help Harry discover and control new powers.
Obviously, Harry Potter himself is the central character. Hermione and Ron are also likely to be important characters as they are Harry's closest friends and often accompany him in his adventures.
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 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.
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.
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.