At the age of 19, Kim Mingyu is told that he is going to get married to the daughter of the Min's, Min Jaekyung to merge the companies together. He realises that his best friend, Lee Haewon, has changed. As he tries to find out why, problems emerged and his life gets complicated. Join Kim Mingyu in the story of Day&Night.

Kim Mingyu

This cold, rich teenage boy is the son of the Kim’s Corporation and a member of the popular group in school called Seventeen. Ever since young, he has  a best friend called Lee Haewon. Their parents are close partners and have been working together before they two were even born. What happens when this teen is set up into an arranged marriage to merge the Kim’s Corporation with another company?

Lee Haewon

This rich but kind girl is the daughter to the Lee’s. Her parents are partners with the Kim’s, whose heir is Kim Mingyu, her  best friend. Being Mingyu’s best friend, she is close to Seventeen, a popular group in Pledis Art High School. Soon after a few years, the Kim’s have decided to merge with another company as they are facing trouble in financial. What happens to her when her best friend is set up into an arranged marriage?

Min Jaekyung

Arranged wife to Kim Mingyu. She is the daughter of the Min’s, who is merging with the Kim’s and Lee’s company to help the companies’ financial problems. To do so, the Kim’s have decided to get their son married to Jaekyung. However, Jaekyung was not happy whenever Lee Haewon is with Kim Mingyu. She finds a way to seperate this two. Will she succeed?

Seventeen

A thirteen-membered boy group consisting Choi Seungcheol(S.Coups), Yoon Junghan, Hong Jisoo (Joshua), Wen Junhui(Jun), Kwon Soonyoung(Hoshi), Jeon Wonwoo, Lee Jihoon(Woozi), Lee Seokmin(DK), Kim Mingyu, Xu Minghao(The8), Boo Seungkwan, Choi Hansol, and Lee Chan(Dino). They are a popular group of boys in Pledis Art High School. Their lockers would always be full with chocolate. They are also friends with Lee Haewon, Kim Mingyu’s best friend.