ONG SEONGWOO - A boy who became one of Fantagio's trainee to chase his big dreams, which is to debut. A boy who then grow to be a charming man was born from a family who is deeply rooted in church. Seongwoo recieved so much love from his family and surroundings that he grow to be a warm hearted man. Ong seongwoo had always wanted a little sister as he is the only child of the family. 

BAEK SEOLHEE - A girl who is raised in a family who is helping the unfortunate, grow to be  a cheerful and caring lady. She had a dream which is to be a make up artist and own her own brand. As the only child in the family, Seolhee had always wanted an older brother by her side. As she graduate from high school, she then entered university and pursue her dream and work as a part timer at a salon.

But they didn't know.

When Baek Seol Hee was born. Seong Woo's dad came up with an idea to arrange a marriage for both of their kid. Their family are very closely related, as their parents are best frieds since they we're young.

Ong Seung Woo and Baek Seol Hee grow as a friend who is very close with each other. They went to the same primary, secondary and high school.

When Seong Woo turns twenty-three, they will held the marriage ceremony and sign it to the government to make it official.

But in his twenty-three, he finally debut as Wanna One's member and will make a debut in acting world which prohibit dating.

What will happen to their relationship when they got the whole world watching?