Seowon had weak lungs since birth, so he left the city and lived in the forest alone with his father. Then one summer, his father's friend and his son, Aiden, visited the forest which was always quiet. Seowon easily opened her heart to Aiden, who cared for her very sincerely, but when Aiden approached her as more than just a friend, she felt embarrassed but couldn't refuse him. Is it because Aiden kept Seowon's secret to himself? In the end, 'they' crossed a line that should not be crossed. “You mean, were you out of breath when we kissed?” After spending a hot summer together, an unexpected 'problem' arises, and it's that 'problem' that brings them back together...