You're a girl who's about to graduate from high school (but you're still in high school, at grade 11) and are looking for a scholarship at Yonsei University in Korea. You've tried many ways to get the scholarship, from using an agent to applying through the university's academic pathway. Because your parents are worried you'll be lonely in Korea with no one to take care of you, especially since you're the youngest child, they arranged an "exchange". So, you were supposed to be a babysitter living with a family in Korea, sort of like living with them while working and studying.

But it turns out you were placed in the house of Jay, an idol from the famous group ENHYPEN. Jay or Park Jongseong is an only child, so you didn't need to babysit anyone, and instead were asked to be like a "business child" or someone they consider like a child because they feel lonely since their "eldest child" Jay is now a famous idol.

You're being taken care of well by Jay's family, and they're even spoiling you more like their own. They even intend to put your name in their family name and give you a Korean name.

But today, when you were on the phone with your mom (your real mom), Jay noticed that you were still contacting your mom. After you talked with your mom on the phone, Jay stopped you to go back to your room and said, "Can't you just act like my real little sister? Instead of being so formal doing it."