It might be a way to show her transformation. Maybe as the story progresses, her glasses falling off is the start of her becoming more involved in the action - packed world of the Avengers and Thor, and she'll become more confident without relying on her glasses as a sort of crutch.
It could be a symbol of her vulnerability. Without her glasses, she might be less able to see clearly, representing her being in a more exposed or less - in - control state in the story.
Maybe she was startled by something sudden, like Thor using his powers or a loud noise. In many fanfictions, characters can be caught off - guard in such situations, causing their accessories like glasses to fall off.
In the fanfiction, when Darcy's glasses fall off, it might be a plot device to create some chaos. For example, she could have been in the middle of an important experiment or task related to Thor's world, like analyzing some Asgardian artifact. Without her glasses, she makes a mistake that sets off a chain of events. Maybe she misreads some symbols on the artifact and accidentally activates a strange power that Thor then has to deal with.
In the fanfiction, after Darcy's glasses fell off, it might have signaled a change in her character's arc. For example, without her glasses, she could have felt more vulnerable, which could have led her to be more open and honest with Thor. This could then develop into a deeper relationship between them, whether it's a friendship or something more romantic. Also, it could be that the act of her glasses falling was a comical moment that lightened the mood in a tense situation involving Thor and some sort of danger or conflict.
He might have been a bit confused at first. After all, glasses are not something he's used to seeing in Asgard. But then he could have quickly reacted with his natural heroism and tried to help her find them.
One idea for this fanfiction could be that Darcy loses her glasses in a chaotic event involving Thor and the Avengers. Without her glasses, she has to rely on her other senses more. Thor, being the noble hero he is, starts to protect her more closely. As they spend more time together, they develop a deeper bond, and Darcy discovers a new side of herself that she was hiding behind her glasses.
She could finally find her glasses and then notice some crucial detail about Thor or a new threat approaching. For instance, she might see a strange symbol on Thor's hammer that she hadn't noticed before.
It could be a simple moment of clumsiness that adds a touch of humor to the fanfiction. Maybe Darcy is in a hurry to see something important related to Thor or the Avengers' activities, and her groping for glasses shows her distracted state.
In a fanfiction, it could be a plot device. For example, as Darcy drops her glasses, she might accidentally discover some hidden clue on the ground that is related to a bigger threat the Avengers are facing. And Thor could be the one to help her make sense of this new discovery, leading to a joint adventure where they have to work together to solve the mystery.
It could be that they fell behind a piece of furniture or were accidentally taken by another character. You'll have to keep looking in unexpected places!
It could symbolize his vulnerability. Without his glasses, Harry can't see clearly, which makes him more defenseless in this chained - up situation.