Perhaps she witnessed something truly tragic or was betrayed by someone she trusted completely. Such intense and negative events could cause her to cry a river.
Maybe she faced a huge heartbreak, like losing someone she deeply loved.
It could be that she faced a huge disappointment, like not getting into her dream school or losing a competition she worked really hard for. Also, heartbreak from a relationship gone wrong could be a reason.
Maybe she lost someone she loved deeply, like a family member or a best friend.
One possible reason is that she is crying out of frustration and then uses dancing as an outlet. For example, if she is having trouble with schoolwork and feels stressed, crying is her initial reaction to the pressure, but then dancing helps her relax.
Often, a lack of proper communication skills can be the root cause. Girls might not know how to express their feelings or resolve conflicts in a healthy way. So, when there is a minor issue like sharing a toy or a difference in opinion, instead of talking it out, they end up in a catfight. And in the midst of all the chaos, a wedgie can happen as a form of aggression during the fight.
She could be crying because she is separated from her parents. Many times at borders, families get split up due to various regulations and procedures.
There could be some medical anomaly. Maybe there is some sort of abnormal connection between the digestive and respiratory systems that could cause air to come out in an unexpected way near the face. But this is highly unlikely.
One possible reason could be bullying. If she was constantly harassed at school or in her social circle, it might have driven her to such a desperate act. Another reason might be family issues, like parental neglect or abuse.
One possible reason could be for ransom. Some kidnappers target girls from wealthy families, thinking they can get a large sum of money in exchange for the girl's safe return. For example, if a girl's parents are business tycoons, the kidnapper might believe they would pay millions to get their daughter back.
One possible reason could be unrequited love. In the fanfic, Chansung might be in love with someone who doesn't feel the same way. This could lead to a deep sense of sadness and cause him to cry. For example, he might have confessed his feelings but been rejected, leaving him heartbroken.
One possible reason could be a misunderstanding or misinformation at birth. For example, if there were ambiguous genitalia at birth, the doctors or parents might have made a wrong assumption about the baby's gender. Another reason could be some kind of psychological experiment by the parents, though this is very unethical. They might have wanted to prove a point about gender being a social construct.