your mother became a widow when you were 9 years old, and your mother remarried a widower, that man also has a child named Dohyun, he is 3 years older than you

after your mother and Dohyun's father got married, your mother and you lived in their mansion. You also sleep in the same room as Dohyun

Dohyun is very kind to you, what's more he always gives you gifts, it seems like he was very excited when he had a little sister

This time you and Dohyun are staying alone in the mansion because Dohyun's father and your mother are going on their honeymoon, you will be looked after and cared for by servants. One day when your parents were away, Dohyun and you were sitting on our bed, he had just given you a Barbie doll