He might meet some old retired wizards who can tell him stories about the old days of magic. For example, they could share tales of how Hogwarts was founded or the great wizarding wars long ago.
In this fanfiction, Harry might go to a magical beach. He could enjoy sunbathing while his magic keeps the sun from burning him. He might also meet some new magical creatures that only come out during holidays.
It could be about how the community in the Harry Potter world comes together to face challenges. Maybe it shows how different characters from the series, like students at Hogwarts, professors, and even magical creatures, work as a group to achieve a common goal, such as fighting against the Dark Arts or protecting the wizarding world.
One great 'Harry Potter Takes Control' fanfiction is 'The Power Within Harry' which shows Harry taking control of his destiny in a unique way. It has him making decisions that are different from the original story, like taking charge of his magical training earlier.
Well, it could be about Harry Potter having a kind heart and taking in various 'strays' in the wizarding world. Maybe he takes in lonely or lost magical creatures, or perhaps other students who don't really have a place to belong. It might explore his nurturing side and how these 'strays' change his life or the Hogwarts environment.
His friends like Ron and Hermione would surely support him. They have been through a lot together, and they believe in Harry's leadership. Also, the Weasley family in general would be behind him. They have always been on Harry's side in his battles against the dark forces.
Maybe it's a possessed object. For example, an old holiday decoration at Hogwarts that has been cursed. The object starts to influence the students and faculty negatively, and in a way, it becomes the main source of conflict, so it can be considered the main antagonist.
Perhaps it's a girl orphan who was found wandering near the Forbidden Forest. She has no memory of her past but shows great potential in potions. Harry feels a connection to her because she seems so lost, just like he once was. So, he decides to take her in as the first orphan in his new orphanage.
In this fanfiction, it could be that Harry takes over the House of Potter to restore its former glory. He might have to deal with dark forces that have been lurking around the property, and he uses his skills and the help of his friends to cleanse it. Maybe he uncovers a plot against the wizarding world that was somehow connected to his family's house, and he has to prevent it from coming to fruition.
In addition to the trio, some fanfictions might focus more on the characters from Slytherin. Draco Malfoy could be a main character in a different light. Instead of being just a rival, he could be an anti - hero or even an ally to Harry. There could also be new original characters created by the fanfiction author that play important roles in the story.