Well, in such a fanfiction, perhaps Felicity is kidnapped by an unknown antagonist. The ponytail pull could be a sign of aggression or a way to control her. Maybe she is being held for ransom, or there's some deeper plot like the kidnapper is trying to get information from her. It could also be that a hero will come to her rescue and the ponytail pull becomes a key detail in identifying the kidnapper later.
The kidnapper might be a mysterious figure who has been stalking Felicity for a while. The ponytail pull could be part of their signature way of handling their victims. It could also be someone who is after a valuable item that Felicity has in her possession.
Well, she could be held in a secret location. Maybe Lopez has some ulterior motives, like getting information from Felicity. He might try to use her skills for his own gain.
Well, it could be that the glasses hold some sort of magical power. Maybe a villain kidnaps them to use that power for evil deeds. For example, the glasses might be able to see into other dimensions, and the kidnapper wants to rule those dimensions.
Perhaps Felicity has a hidden power that is only activated when she has her glasses. Without them, she has to find an alternative way to fight back against her kidnappers. This could lead to her developing new skills or alliances within the story.
Maybe Felicity has to go on an adventure to find her glasses. She could meet some interesting characters along the way who help or hinder her search.
One possible plot could be that Felicity has some sort of vendetta against the person with glasses. Maybe she kidnaps them to get information. For example, if in the fanfiction's universe the person with glasses has access to some secret technology or knowledge that Felicity desperately needs for her own purposes, like to save a loved one or stop a greater evil. So she resorts to this extreme measure of kidnapping.
Well, it could be a symbol of a past encounter. Maybe the person who was kidnapped was wearing the ponytail and the kidnapper took the hair tie as a sort of trophy or reminder. It might also be used by the protagonist later on to identify the kidnapper, like if they notice the hair tie on the kidnapper's wrist during a chase or confrontation.
The character Felicity could be a complex anti - hero type. She might be someone who has been pushed to the edge by circumstances in the fanfiction world. The person with glasses could be a nerdy scientist type. They could be working on a project that Felicity believes is dangerous if it falls into the wrong hands, so she kidnaps them to either stop the project or control it herself.
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.
In the fanfiction, Felicity with her hair in a bun might find a way to escape on her own. Since her hair is in a bun, she could use the hairpin or ribbon in it to pick a lock or create a distraction. Once she escapes, she has to evade the kidnappers' search parties while trying to find her way back to safety. Along the way, she might meet some unexpected allies who are drawn to her because of her unique appearance, including her bun.