Sehun lives in Jeju Island, where the Kang and Oh's started having vacation every summer when both Seulgi and Sehun were 8 years old. The two kids grow up together, side by side, for three months out of the year before Seulgi leaves at the end of each summer to head back home to Seoul.

As they get older, their relationship changes and matures and all it takes is three months to ultimately change their relationship, and their lives, forever.