Well, it might be that Harry decides to go stag because he doesn't want to be tied down by the traditional ball - going - with - a - date idea. At the ball, he might discover a new side of the event, like exploring parts of the venue that are usually overlooked. He could also end up helping out some other students who are in a bind, which would show his kind nature.
He might interact with Luna Lovegood. She's always open to new and interesting conversations, and she could approach Harry when she sees him alone.
In this fanfiction, they might have a really magical time at the Yule Ball. Maybe they start off a bit awkwardly, as Harry is often shy in such social situations. But Luna's unique charm could put him at ease. They could share a slow dance, and Luna might point out some of the strange and wonderful magical creatures that are part of the ball's decorations to Harry.
Well, it could be that Harry goes to France on a secret mission. Perhaps he's following a lead on a dark wizard who has ties to France. In France, he might have to adapt to different magical customs while trying to complete his mission.
Maybe Harry goes to Canada to study magic in a hidden Canadian wizarding school. He could meet new friends and learn about different magical creatures native to Canada, like the Thunderbird.
In this fanfiction, perhaps Harry is sent to Beauxbatons as part of an exchange program. At Beauxbatons, he might face some challenges due to the different culture and magic styles. He could also get involved in a mystery related to the school's history, for example, an ancient spell hidden in the school that only he can solve with his unique perspective from Hogwarts.
The plot could involve Harry going to Harlem in search of something specific, perhaps a magical artifact if we're adding a bit of magic to the fanfic. Along the way, he meets interesting characters who help or hinder his search. He could also experience the different food and art in Harlem, which changes his perspective on life.
Well, perhaps Harry Potter goes to Dalton and discovers a whole new world of magic there. Maybe he meets new friends and has to face different challenges compared to Hogwarts.
Well, it could be about Harry using his magic skills in the Elemental Nations. Maybe he'll learn new forms of magic there or make new friends with people who have elemental powers.
In this fanfiction, it could be that Harry Potter has a vision of a future where Voldemort has completely taken over the wizarding world and killed all his loved ones. This drives him into a state of madness and he goes on a rampage. He travels back in time using some ancient magic he discovers, and starts to take out all the Death Eaters one by one, not caring about the consequences, as he believes it's the only way to change the future.
One possible plot could be Harry struggling to adapt to the strict discipline of military school at first. He might have conflicts with the drill sergeants who are tough on him. But as time goes by, he discovers his own inner strength and leadership skills, and eventually earns the respect of his peers and instructors.