Lee Myeongyi has spent his entire life living with pneumothorax, a collapsed lung. He loathes the attention he attracts at school due to his episodes of loud hyperventilation, prolonged coughing fits, and exemptions from both physical education and military service. Whether enduring the curiosity or anger of his classmates, Myeongyi feels like a total outcast. However, class president Han Seonho frequently displays kindness and understanding toward Myeongyi. Through his friendly gestures and handsome appearance, Seonho becomes Myeongyi's first crush. Nine years later, Myeongyi attends his high school reunion for a single reason: to see Han Seonho again. He harbors a faint hope regarding the other man's feelings for him—but upon noticing the bright gold ring on Seonho's left hand and hearing his classmates' intrusive questions, that hope is swiftly crushed. Excusing himself to go smoke, despite the condition of his lungs, Myeongyi is followed outside by Seonho. Unexpectedly, this marks the start of their illicit love affair.