Obviously, Harry Potter himself would be at the center of it. His friends Ron and Hermione would likely be involved too. They might be trying to protect Harry or stop him from getting into more trouble. Also, Draco Malfoy could be involved. He might take advantage of Harry's lack of glasses and start a fight, thinking he can easily defeat Harry when he's not seeing clearly.
In a 'Harry Potter without glasses brawl' fanfiction, it could start during a Quidditch match. Without his glasses, Harry can't see clearly. He thinks an opposing team's player is trying to cheat in a really aggressive way and he jumps into a fight mid - air. This could lead to a huge brawl between the two teams. And the Ministry of Magic might get involved later to sort out the mess.
Harry could be at a significant disadvantage without his glasses. He might misjudge distances when Nagini attacks, making it more dangerous for him. However, this could also lead to the discovery of new magical abilities, like a form of magic - based echolocation. Nagini might be used by the dark forces to take advantage of Harry's impaired vision.
Perhaps it's an old enemy from Harry's past, like Draco Malfoy who has turned to the dark side completely. He blames Harry for all his misfortunes and decides to cage him without his glasses as a form of cruel punishment.
Voldemort or his Death Eaters are likely antagonists. They have always been out to get Harry, and chaining him up without his glasses would be a cruel and effective way to subdue him.
It could be the Death Eaters. They might see Harry as a big threat, and by caging him up without his glasses, they aim to make him vulnerable. They know his glasses are an important part of his identity and his ability to see clearly in the magical world, so they take that advantage away from him.
The plot could progress with Harry using magic to compensate for his lack of glasses. For example, he could use a spell to make his eyesight better. Or, his friends could use their skills to help him. Hermione might use a spell to locate his glasses in the chaos of the brawl.
In such a fanfiction, Harry might be at a serious disadvantage. Without his glasses, he'd struggle to see clearly. His opponents could easily take advantage of his impaired vision. He might have to rely more on his other senses, like his hearing or his magical intuition. Maybe he'd cast a spell to enhance his vision temporarily, but it could backfire or be disrupted during the brawl.
In fanfiction, if Harry Potter were without glasses, it would likely have a significant impact on his character arc. His glasses are not just a visual accessory but also a symbol of his 'nerdy' or 'outsider' status at the start. Without them, he could be more integrated into the 'cool' crowd at Hogwarts. He might also be more daring in his adventures as he wouldn't have to worry about his glasses getting broken or lost during battles or dangerous situations. This could lead to a more confident and perhaps even a more flamboyant Harry Potter in the fan - created stories.
A fanfiction idea could be that without his glasses, Harry's world becomes a bit of a blur. He starts to rely more on his other senses. In the Forbidden Forest, this could be both dangerous and enlightening. He might be more attuned to the sounds and smells of the forest, but at the same time, he could easily walk into a dangerous area. His friends, Hermione and Ron, would have to be extra vigilant in protecting him. This new dynamic could change the relationships between them and lead to new adventures.
One possibility could be that in this fanfiction, Harry's glasses are some sort of magical anchor. Without them, he might accidentally slip into a different dimension. Maybe he was in the middle of a battle at Hogwarts, his glasses got knocked off, and suddenly he vanished. It could be that the glasses were enchanted by Dumbledore long ago to keep Harry in the 'right' magical space, and without them, he's lost in a sort of limbo.