Perhaps Voldemort's pet has a strange connection to Harry's glasses. Maybe the glasses hold some sort of magic that the pet is drawn to. In the fanfiction, the pet might try to use the glasses' magic for its own evil purposes, and Harry has to stop it.
One possible plotline could be that Voldemort's pet somehow steals Harry's glasses as a way to taunt him. This could lead to Harry going on a quest to retrieve them, facing various dark magic obstacles along the way.
Perhaps Voldemort uses magic to brainwash Harry into thinking he is his pet. Harry then has to fight against this false identity while still being under Voldemort's control. The plot could involve Harry slowly regaining his true self and using his new - found knowledge of Voldemort's inner workings (from being so close to him) to defeat him in the end. It would be a journey of self - discovery and resistance.
In some fanfictions, Voldemort's pet might be used as a symbol of his power and evil. Harry's glasses, on the other hand, are an iconic part of his character. The combination could be used to create a unique plot. For example, Voldemort's pet might steal Harry's glasses to disrupt his vision and thus his ability to fight. It could also be a more symbolic connection, like the pet representing Voldemort's hold over Harry's life, and the glasses being a symbol of Harry's identity that Voldemort wants to break.
The fanfiction could explore a scenario where Harry's glasses are taken away as a way to break his spirit. Voldemort, having Harry as his pet, might want to completely subdue him. Without his glasses, Harry has to navigate a blurry world. This could lead to some interesting interactions with other characters. For example, Hermione might try to find a magical way to restore Harry's vision or at least give him some form of sight assistance without glasses. Ron, on the other hand, could be conflicted about whether to help Harry escape Voldemort's clutches or if he should follow Voldemort's orders as well since Harry seems so different without his glasses.
Maybe in this fanfiction, Voldemort has a change of heart after making Harry his pet. Without his glasses, Harry appears more helpless, and this could stir some long - forgotten emotions in Voldemort. He starts to see Harry not just as an enemy but as someone he can manipulate in a different way. He could try to groom Harry to be on his side, using a combination of threats and false kindness. Harry, on the other hand, is constantly thinking of how to turn the tables and get back to his friends and the fight against the Dark Lord.
One possible plotline could be that Voldemort captures Harry early on and instead of killing him, decides to keep him as a pet. Harry, being in this strange situation, might start to develop a warped sense of loyalty to Voldemort over time.
One possible plotline could be Harry being held captive by Voldemort in a way that's like a pet. Voldemort might use Harry to show his power over the Boy Who Lived. Another could be that Harry has some sort of magic that makes Voldemort keep him as a pet instead of killing him immediately.
It could be that the pet is magically attracted to the glasses. Maybe the glasses have a certain charm or power that the pet senses, and it tries to steal them to bring back to Voldemort. For example, if the glasses can see through certain dark magic disguises, Voldemort would want to get his hands on them through his pet.
The pet could try to break Harry's glasses. Since Voldemort hates Harry, his pet might be programmed or trained to destroy things that are important to Harry. The glasses are a very visible and important part of Harry.
Perhaps Snape, in a moment of weakness or out of some deep - seated sense of responsibility, decides to protect Harry in an extreme way. He treats Harry like a pet in that he provides for all of Harry's needs but also restricts his freedom. This could lead to a lot of internal conflict for Harry, who is used to being independent. Meanwhile, Snape has to deal with the other characters in the wizarding world who might not understand his motives for treating Harry this way.
It could be that Voldemort's pet Harry is actually a form of psychological warfare for Voldemort. He wants to break Harry's spirit completely. However, Harry uses this situation to his advantage. He befriends some of the dark creatures that Voldemort has around his lair, and with their help, he manages to create chaos and confusion, which in turn gives the Order of the Phoenix an opportunity to strike at Voldemort.