Family dynamics could be a theme. There could be things she keeps secret because of the complex relationships within the family. For instance, if there is a lot of competition among siblings, she might hide her achievements or failures.
One main theme could be self - discovery. She might be on a journey to find out who she really is, away from the expectations of her family and society, and this process is full of secrets.
The theme could also be about personal growth. The sister might have overcome some great obstacle in secret, like dealing with an illness or a difficult situation at school or work. And this secret experience has made her grow as a person. It could also be about friendship, where she has a secret friendship that has influenced her in ways her family doesn't know, and this friendship is an important part of her real - life story.
Well, the sister herself is obviously a main character. And perhaps her best friend who might be the only one she has confided in about her secret.
It could be about betrayal. Maybe someone betrays a secret that was supposed to be kept, and the whole story revolves around the consequences of that betrayal.
It could involve a secret friendship. She might have befriended someone who was considered an outcast in society, and she didn't want her family to know because of the potential judgment. So she maintained this friendship in secret throughout her life.
The theme might be redemption. Suppose Cindy made some mistakes in the past and her secret story is about how she is trying to make up for those mistakes and redeem herself in her own eyes and the eyes of others. She might be secretly doing good deeds or facing her past demons to achieve this redemption.
One possible main theme could be secrecy itself. The whole story might revolve around how Terrius keeps certain things hidden and the consequences of that secrecy.
It could be about friendship. Many life stories revolve around the relationships we build with others, and friends play a big role in our lives.
It could be loyalty. Dogs are known for their loyalty, so the story might revolve around a dog's unwavering loyalty to its owner or a particular person.
I don't know for sure. But I assume the sister is one of the main characters. There might also be other family members like her parents, brothers, or other sisters who could be important in the story since it's about a sister's secret.
Another theme might be the power of imagination. The story could show how the little sister's vivid imagination creates this entire world full of magic and mystery. She might use her imagination to transform a dull day into an exciting adventure, and the story could be about how important it is to have an active imagination in our lives.