While Se-jin is on her way to the address listed on Seung-wan's passport, she meets Min Do-hyun (Lee Ji-hoon), who kindly gives her a piggyback ride.

A year later, Se-jin's older sister crashes Seung-wan's father's birthday party, carrying his daughter, Shin-bi (Jung Da-bin).

Their parents force Seung-wan and Se-jin to get married for the baby's sake, but the two draw up a list of rules that they must abide by, including the freedom to pursue their own careers and individual love lives, as well as a possible divorce in five years' time.

Seung-wan takes a job in his father's construction business to support the family, but is forced to leave for mandatory military service shortly after.

But when Shin-bi is diagnosed with leukemia and Seung-wan and Se-jin desperately search for a viable bone marrow donor, they realize how much they love each other and the family they've created.