Perhaps the girl without glasses has a special ability that she's not fully aware of. The kidnappers, who are part of some sort of secret organization, know about this ability. They kidnap her to study her or use her power for their own purposes. As she's held captive, she starts to discover more about this ability herself and tries to use it to escape.
One possible fanfiction could be that the girl who was kidnapped was a very shy and nearsighted person. Without her glasses, she could barely see. The kidnapper might have targeted her because of some special ability she unknowingly had. As she was squinting in the dark place where she was held, she started to recall all the mystery novels she had read, trying to find a way to escape using the little she could see and her wits.
There could be a heroic rescue. Maybe her friends or family notice she's missing quickly. They start looking for her and manage to track down the kidnappers. Since she doesn't have her glasses, she has to rely on her other senses like hearing to help her stay alive until she's rescued.
The kidnapper could be a jealous rival. Maybe in the story's setting, there's a competition of some sort, and the girl without glasses is a threat to the rival. So, the rival decides to kidnap her to eliminate the competition.
One possible plot could be that the girl is kidnapped from a place where she left her glasses behind. She is a key figure in a certain event, and the kidnappers want to use her for their own gain. Without her glasses, she struggles to adapt to the new environment at first. However, as time passes, she befriends another captive who helps her get around. Together, they plan an escape and in the process, she discovers that there's more to her kidnapping than she initially thought.
I'm not sure which specific 'Kidnapped Felicity Squints Without Glasses' fanfiction you're referring to. There could be many different interpretations and stories within that concept. Maybe it's about Felicity being kidnapped while in a situation where she's not wearing her glasses and has to rely on other senses or the help of others to escape.
In this fanfiction, Blurry without glasses might be on a quest to rescue Felicity. Their journey could be filled with obstacles not only because of the danger of the kidnappers but also because of their impaired vision. This could lead to some really intense and exciting scenes as Blurry tries to navigate and find Felicity.
Another possibility is that a mysterious character in the fanfiction world, who has a soft spot for the girl, finds her lost glasses. He then uses this as a clue to track down where she has been taken. Along the way, he discovers more about the girl's situation and the reasons behind her kidnapping.
If this is a fanfiction, it might explore themes of vulnerability and heroism. Felicity being kidnapped puts her in a vulnerable position. Blurry without glasses could be seen as less capable at first, but perhaps they overcome this disadvantage to rescue Felicity. It could also involve a lot of character development for both Felicity and Blurry as they face this difficult situation.
She could use her memory of the environment before she lost her glasses to her advantage. For example, if she knew there was a particular landmark near the place she was kidnapped from, she could try to move in that direction once she escaped the immediate area where she was held.