The story could start with the girl going about her normal day, the hair tie casually on her wrist. Then suddenly, she's grabbed and taken away. The hair tie might play a role in her escape plan. For example, she could use it to leave a trail or as a tool to pick a lock if it's long enough and strong enough.
The fact that her hair is in a bun might also play a role. It could be a cultural or traditional style in the fictional world she belongs to. When she's kidnapped, her captors might be disrespectful of this style, which angers her and gives her the motivation to resist. The bun could also be used practically during her captivity. For example, she might hide small objects in it to help her escape, like a lock pick or a small note.
In fanfiction, a girl with a dirty hair tie on her wrist could be a sign of her being in a hurry or perhaps she's been through some sort of adventure. Maybe she was so caught up in an event that she didn't have time to clean up or change her hair tie. It could also be a unique characteristic given to her by the author to make her stand out. For example, in a fantasy fanfiction, it might be a charm that has some special power but just looks like a dirty hair tie.
A disgruntled ex - friend could be the kidnapper. Maybe there was a falling - out between the two characters, and the ex - friend wants to get back at the owner of the hair tie. They think that by taking this precious item, they can cause emotional pain.
Perhaps the girl was kidnapped because she was wearing the hair tie in a certain way that is significant to a cult or a secret society. They believe she is a chosen one or something similar. As she's held captive, she learns about their strange beliefs related to the hair tie and tries to use that knowledge to turn the situation around and free herself.
One idea could be that the hair tie is a secret signal among a group of friends. When the main character has a hair tie on their wrist, it means they are in trouble. Their friends notice it when they are kidnapped and start a rescue mission. They follow the clues left by the kidnapper which are somehow related to the hair tie.
One possible plot could be that the hair tie has some sort of magical or sentimental value. Maybe it was given to the main character by a loved one. A villain kidnaps it to try and manipulate the character into doing something. The character then has to embark on a quest to get it back, facing various obstacles along the way.
Well, first, establish the character who has the hair tie on their wrist. This character could be a very popular or important person in the fanfiction world. The kidnapper might target them because of their status. During the kidnapping, the hair tie could get damaged, which adds to the tension. The character then has to find a way to repair it or use it in its damaged state to escape. For instance, they could use a broken part of the hair tie to cut through ropes if it's made of a strong material. The hair tie can also be a connection to other characters. For example, another character might see the hair tie on the news when the kidnapping is reported and recognize it as belonging to the kidnapped character, which then sets off a chain of events to rescue them.
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.
In a fanfiction, the girl with the hair tie on her wrist is on a solo hike. She uses the hair tie to mark the trees along the way so she can find her way back. But then she gets lost. As she tries to retrace her steps, she realizes that the hair tie is not just a simple accessory but a reminder of her own strength and she manages to find her way back to the main trail.
The hair tie on the girl's wrist in the rain could be a symbol of a past relationship. Maybe it was given to her by an ex - boyfriend, and as she stands in the rain, she is reminiscing about the good times they had. Every time the raindrop touches it, it brings back a memory.