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!
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.
One possibility could be that in this fanfiction, Darcy without glasses might have a more confident and alluring look. She could catch Thor's attention in a new way. Maybe she's at an Avengers party and without her glasses, Thor mistakes her for someone else at first, leading to an interesting encounter.
Maybe Thor, being the chivalrous god he is, might pick up Darcy's glasses for her. He could use this simple act to start a friendly conversation with her, perhaps asking about the purpose of these strange 'eyeglasses' as they don't have such things in Asgard.
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.
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.
Well, an idea could be that Darcy is swimming in a pool when suddenly her glasses get knocked into the water. Since her glasses are important to her, she dives in to get them. Meanwhile, the Avengers are having a meeting nearby. Hawkeye spots her struggling in the water and alerts the others. Captain America jumps in to save her and retrieve the glasses.
She might be more adventurous. Without glasses, she could be bolder and join Thor on his quests more readily. For instance, when Thor is looking for a certain relic on Earth, Darcy without glasses might be the first to volunteer to help, seeing it as an opportunity to prove herself.
Well, she might have trouble seeing clearly. Maybe she stumbles around a bit, which could lead to some comical situations. For example, she could accidentally bump into Thor or other characters, causing some light - hearted banter.
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.
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.