A group of thieves could be the kidnappers. They were planning on robbing Daria's house but found her there instead. They take her with them to avoid being caught and in the rush, her glasses are lost. They might keep her hostage until they figure out what to do with her, all the while Daria is trying to figure out how to escape and get her glasses back.
Perhaps it's a jealous rival. Maybe in the world of this fanfiction, there's some sort of competition, like for a job or a love interest. And this rival decided to kidnap Felicity to get her out of the way.
It could be a group of rogue Death Eaters who think that kidnapping Harry would bring them back into Voldemort's good graces. They might take his glasses as a way to humiliate him, seeing Harry as the symbol of their defeat. They underestimate Harry's resourcefulness even without his glasses.
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 possibility is that the kidnapper is an ex - partner or an ex - friend who has turned bitter. They might feel betrayed by the girl with glasses in some way and think that kidnapping her is the best way to get back at her. Another likely candidate could be a character from a parallel story or an alternate universe who has some sort of vendetta against the girl. For instance, if there are different factions in the fanfiction world, and the girl with glasses is on one side, someone from the opposing side might kidnap her to gain an advantage. Additionally, it could be a self - proclaimed vigilante who believes the girl is involved in something wrong and takes it upon himself to 'punish' her by kidnapping her.
It could be a jealous rival. Maybe someone who is envious of Felicity's intelligence or her relationships. Without her glasses, this person might think she's more vulnerable and easier to manipulate or hold hostage to get what they want.
It could be a jealous rival of Felicity. Maybe someone who is envious of Felicity's intelligence which is somehow related to the glasses. So they kidnap the glasses to try and bring Felicity down.
It could be a jealous rival. Maybe someone who is envious of Felicity and wants to cause her trouble by taking her glasses.
One possible plot could be that Daria is kidnapped by a group who mistake her for someone else. In the chaos of the kidnapping, her glasses are lost. As she's held captive, she has to rely on her wits more than ever without her glasses to see clearly. She might start to analyze her captors' behavior and motives, trying to find a way to escape. Maybe she uses her sharp tongue and intelligence to outwit them, all while dealing with the inconvenience of not having her glasses.
It could be an old enemy of Keith's, someone from his past who has a vendetta against him. Maybe a former rival from his days in the military academy who has now turned to more devious means.
In some creative fanfiction, it could be an alternate version of Spiderman himself from a different dimension. This Spiderman has gone bad and kidnaps a fan from our dimension as part of some grand, dark plan that involves crossing dimensions and causing chaos.