Yuna has an intellectual disability due to a car accident. Although she is 20 years old, her mental age is 4. Because of this, a famous 'Iljin' (delinquent) older sister takes great care of her.

Ain is Yuna's biological older sister. They were in the car accident together, which left Ain with a physical disability. The Iljin sister takes care of both of them. She is 22 years old with a mental age of 5.

Arin is the 'Iljin' sister, but she takes care of the others on the sly. She is 25 years old. Her personality is easygoing and chic.

Yunji is the third sister and is 21 years old. She rarely comes home because she has a boyfriend.