A fanfiction could start with Harry's glasses being stolen by a mischievous house - elf. Harry starts to squint to see in his classes, which causes some problems. For instance, in Potions class, he misreads the instructions and creates a minor explosion. He spends the day trying to find the house - elf and his glasses. Along the way, he meets some other characters who help him in unexpected ways. By the end of the day, he gets his glasses back and has learned a valuable lesson about not taking his eyesight for granted.
One possible fanfiction could be that Harry loses his glasses during a Quidditch match. He has to squint to see the Snitch, which leads to some comical near - misses and some very frustrated team - mates. In the end, he manages to find his glasses just in time to catch the Snitch and win the match.
Perhaps Harry discovers that his loss of glasses is part of a magical curse and he has to break it to get them back and restore his vision.
Maybe it's a jealous student from Hogwarts. Someone who is envious of Harry's fame and power. This student has been studying dark magic in secret and decides to kidnap Harry to prove that they are better. They take his glasses to humiliate him as well. They might think that without his glasses, Harry is just an ordinary wizard and they can easily overpower him.
A simple plot could be that Harry's glasses break right before an important exam. He has to squint to read the questions, which makes it really difficult for him. His friends try to help him, but the examiner doesn't allow any outside assistance. Harry has to dig deep and rely on his memory of the material to get through the exam. In the end, he passes, and it shows his determination.
One possible fanfiction could be about Harry having trouble with his glasses after a spell goes wrong. He has to squint constantly to see clearly, and this leads to some comical situations at Hogwarts. For example, he mistakes a cat for a Kneazle during Care of Magical Creatures class.
A possible plot could be that Harry is framed and sent to Azkaban. Without his glasses, he struggles to see clearly. One day, he finds an old magical object in his cell. He tries to figure out what it is by using his other senses. As he explores it, he starts to unlock some of its secrets which could be the key to his escape or a way to expose the real culprits behind his false imprisonment.
Another reason might be related to a new magical artifact or potion. Harry might have come across something that had an unforeseen effect on his glasses. It could be that a new charmed item he was using interacted with his glasses and caused them to disappear.
One possible plot could be that a dark wizard kidnaps Harry Potter in order to steal his powers. In the chaos of the abduction, Harry loses his glasses. Without his glasses, he has trouble seeing clearly which adds to his vulnerability. The wizard might be working for Voldemort or could be a new enemy. His friends Hermione and Ron would then embark on a quest to rescue him. They would face many challenges along the way, like getting past dark magic traps and finding the location where Harry is being held captive.
There could be a fanfiction where Harry is studying in the library with his broken glasses. He's squinting hard to read the old, faded texts. Hermione notices and offers to help him fix his glasses with a spell she's been researching. But Harry refuses at first, wanting to do it on his own. This creates a bit of tension between them, and as they argue, Ron comes in and tries to mediate. It could be a comical and character - driven fanfiction scenario.
Well, it could start with Harry being lured into a trap by some mysterious enemies. They might be after the secrets of Dumbledore's Army or something. Once trapped, they start torturing him. His glasses could be lost when he's thrown around during the torture. Then, he might use his magical skills, like his ability to communicate with snakes (which he has from being a Parselmouth), to call for help or find a way to escape. He'd be at a disadvantage without his glasses, but his determination would keep him going.