Gazing at the scenic view of the sky, a man is joined by a stranger who informs him that he is in a dream. Unable to recall the memories of his life, he relies on the visitor to take him on a journey of discovery. Revealing everything—from their seven-year relationship to the emotional hardships they faced together—the two rekindle their bond severed by time. Behind this beautiful love story, however, lies a much darker truth.

Lee Myeongyi has lived his whole life with pneumothorax—a collapsed lung. He despises the attention he draws at school with his bouts of loud hyperventilating, extended coughing fits, and exemption from physical education as well as military service. Whether suffering through the curiosity or ire of his classmates, Myeongyi is left feeling like a complete outcast. However, the class president Han Seonho often shows Myeongyi kindness and understanding. With his friendly gestures and handsome looks, he becomes Myeongyi's first crush. Nine years later, Myeongyi attends his high school reunion for only one reason: to see Han Seonho once again. He holds a tiny glimmer of hope about the other man's feelings for him—but after seeing the bright gold ring on Seonho's left hand and listening to their classmates' prying questions, that hope is quickly dashed. Excusing himself to go take a smoke, regardless of the state of his lungs, Myeongyi is followed outside by Seonho. Unexpectedly, that marks the beginning of their illicit love affair.

Underneath the bright city lights lies a bloodied arena bursting with frantic screams and roars. Strong men engage in boxing matches for money, while their audience desperately hopes that their chosen participants will bring them fortune. For the young rising star Mignon, there is only one place that is an escape from the chaos of the ring and his tough life. Mysterious underground doctor Oh Young-One offers his services to injured fighters, and the wide-eyed Mignon finds solace in his quiet infirmary. Young-One is gentle and caring, always tending to Mignon's wounds that mainly come from the cruel world beyond the boxing ring. However, the doctor hides a taboo secret about himself. In a rare moment of carelessness, he exposes it to Mignon, putting his life in immediate danger. Even though Young-One warns Mignon to keep his distance in order to protect him, Mignon remains stubborn and refuses to abandon the one person who makes him feel as though he truly matters.