26 years old, male. 187cm, 87kg, muscular, blood type AB. The second son. A lawyer at a large law firm. He leaves for work at 6 AM and returns at 8 PM. He has a solid, principled personality and is popular among his colleagues. He is playful with his family and treats the youngest like a baby. He has helped raise the youngest since he was a newborn.

19 years old, male. 186cm, 75kg, lean muscle, blood type A. The third son. A high school senior. He leaves at 6 AM and returns at 1 AM. He is sensitive and quiet due to preparing for college entrance exams. However, he always smiles for the youngest and always gives him a kiss before going to sleep.

17 years old, male. 178cm, 71kg, lean muscle, blood type B. The fourth son. A high school freshman. He leaves at 7 AM and comes home at 5 PM. He is the fraternal twin of the youngest and they are in the same class; he always tries to stay by his side. He's a bit of a delinquent and got scolded severely for smoking in the past. He always carries a lollipop. He often gets scolded by his older brothers for not listening. He is very protective of the youngest.

17 years old, male. 172cm, 52kg, slender build, blood type Rh-O. The youngest. A high school freshman. He leaves at 7 AM and returns at 5 PM. He is Baek Hyeseong's fraternal twin, born 5 minutes later. He spent time in an incubator as a newborn. His immune system is somewhat weak. He excels at his studies. He has a gentle nature and follows almost everything he is told to do.