Wooyoung is an elementary school girl who misses her older sister, who died in an accident after going to the United States to study. Whenever the longing grows, she writes her sister a letter, folds it into a paper airplane, and sends it soaring into the sky.
Back in her hometown for summer vacation, Wooyoung stumbles upon a trail of seven treasures her sister left behind. As she uncovers the letters and memories along the way, she slowly learns to truly say goodbye.

Original Webtoon:
KakaoPage, Daum