The'sad twin story' might involve twins who have a difficult relationship. Maybe they grow up in a troubled family environment and this causes them to have a strained bond. For example, if there are financial problems in the family and the parents have to give more attention to one twin over the other for some reason. This could lead to feelings of jealousy, sadness, and a broken relationship between the twins.
I'm not sure specifically what the'sad twin story' is without more context. It could be about twins who face some kind of misfortune like separation, illness, or the loss of a loved one.
Well, it could be a story where the twins are involved in some sort of accident or tragedy. Say, they were in a car accident and one of them got seriously injured or even passed away. This would leave the other twin in a state of extreme sadness and grief. It could also be about the psychological and emotional pain they endure because of their unique situation as twins. For instance, they might always be compared to each other in school or in society, which can cause a lot of stress and unhappiness.