They are not unrelated. Xiaojun was adopted by his parents. Xiaojun's parents just got married and later adopted Xiaojun in an orphanage because they were infertile. Xiaojun's father was a college art teacher, and later divorced his student Mei Yuge and his mother. Xiaojun's father married Mei Yuge and had his own child Xiaomei, who was adopted by his father. They are not related by blood. The wrong love for Xiaojun's sister was born by Xiaojun's father and stepmother.