Stats | 175cm • 67kg A 16-year-old boy with calm, transparent eyes. He suffers from Alexithymia (inability to express emotions), which sometimes leads to him being unfairly criticized, but he has lived a peaceful life surrounded by the love of his mother and grandmother. However, he loses his grandmother in a stabbing spree on Christmas Eve, and his mother ends up in a vegetative state. Afterward, he runs the second-hand bookstore they used to own by himself, occasionally visiting the hospital to check on his mother. He thought he was alone, but thanks to the protection of 'Dr. Shim,' an acquaintance of his mother, he was able to live safely. One day, 'Professor Yun' visits him. He is asked to act as the professor's long-lost son for his dying wife. Yunjae accepts and stays by her side until her death. A few days later, at her funeral, he finally comes face-to-face with the real biological son, 'Goni.'

Stats | 163cm • 43kg A small, scrawny boy with dark skin. As a child at a facility called Huimangwon, he gave himself the name 'Goni' and told everyone to call him that instead of Isu. He transfers to Yunjae's class, but due to his crooked behavior, he is labeled a troublemaker from day one. He was found by his family after 13 years of being missing since age four. During that time, he was kidnapped and raised by illegal immigrants, who abandoned the children and fled when pursued by authorities. He bounced between orphanages, was adopted only to be dissolved two years later, returned to an orphanage, and eventually became a juvenile delinquent who ended up in a detention center. He is a tragic figure whose heart was broken by too much pain, though he is not inherently bad. He harbors a grudge against Yunjae for meeting his mother—whom he hadn't seen since childhood and couldn't even remember—in his place, and he bullies Yunjae until he gets suspended. However, upon realizing that Yunjae felt no ill will toward him due to his Alexithymia, he begins visiting Yunjae's bookstore frequently and gradually grows close to him.

Stats | 176cm • 68kg A relaxed smile and an intellectual impression. The owner of 'Shim Jae-young Bakery' located above Yunjae's bookstore, and the owner of the building itself. He was originally a cardiac surgeon at a university hospital but changed careers. He takes on the role of Yunjae's guardian after Yunjae is left alone. He suggests that Yunjae continue running the bookstore for a salary to cover living expenses, while saving the grandmother's life insurance money. He helps Yunjae navigate school and try to feel emotions. Though Yunjae didn't know it, he was a friend of Yunjae's mother and knew a lot about him through their conversations. He is a great benefactor in Yunjae's life.

Stats | 178cm • 69kg Not a 'bad person,' but someone who failed to understand his own son. Yun Isu's father. Yunjae refers to him as Professor Yun. He teaches business administration at a university and is quite wealthy, living in a top-floor apartment with a Han River view. He first met Yunjae in a hospital elevator. Later, he visited Yunjae's bookstore, where he introduced himself. He scolds Isu when Isu wrongs Yunjae. His relationship with Isu is very poor. He couldn't hide his disillusionment when the son he had searched for so long appeared as a delinquent. Ultimately, for the absurd yet somewhat understandable reason that he couldn't show his wife a son who was so far from 'the son they dreamed of,' he presented Yunjae—who resembled Isu—to her instead. In doing so, he permanently robbed his son of the chance to reunite with his biological mother. Furthermore, he never tried to truly understand what kind of life his son had lived and failed to believe him when he was treated unfairly.

Stats | 160cm • 49kg A lively and bold girl. Yunjae's classmate. She usually wears silver-rimmed glasses, but the fact that she doesn't wear them when running suggests her eyesight isn't severely poor. She loves and excels at sports, especially running. Sometimes she even leaves class to exercise alone in the gym. She actually wanted to go to a physical education high school rather than a regular one, but her parents opposed it. After meeting Yunjae, she becomes close to him by visiting his bookstore often, and Yunjae begins to feel emotions he has never experienced before because of her.