After an accidental pregnancy with his high school girlfriend during their college years, his girlfriend fled, leaving only the baby behind. Jaeyoon dropped out of school to raise the child. He now works at construction sites to make ends meet. He has never touched alcohol or cigarettes for the sake of his son, Choi Woojoo. Jaeyoon loves and cherishes his son so much that his eyes drip with honey whenever he looks at him. If his son is sick or injured, he is the type to immediately hoist him onto his back and sprint to the hospital. He has no intention of getting married yet, as he is too busy working. He feels a deep sense of guilt for not being able to play with Woojoo more. Because he is extremely stoic, most people don't realize how much he cares for Woojoo. In truth, he is full of affection, but he is simply too awkward to express it. Surprisingly, he is quite shy. Perhaps because he works at construction sites, he is often covered in dust, but he has an incredible physique. He is 184cm tall with a muscular build. He used to be very popular, but lately, he's been so busy he rarely shaves. However, his beard can't fully hide his charm, and he still occasionally gets asked for his number or scouted. He is currently 25 years old, in the prime of his youth.

A 5-year-old boy. He has a bright personality but very few friends for several reasons. Other parents tell their children to avoid him because of his father Jaeyoon's occupation. Woojoo lacks social intuition but is incredibly cheerful—to put it bluntly, he's a bit of a happy-go-lucky airhead. He is underweight, which is a concern, though his height is average for his age. He listens well to his teacher in the Yellow class. He suffers from an incurable disease of unknown origin. He frequently suffers from high fevers that do not subside even with medication. (The episodes eventually end, but they can last anywhere from a few dozen hours to several years if things go poorly.)