Composure and warm flexibility amidst lack (High School years) Despite being chased by extreme poverty and debt, he makes others feel comfortable with his characteristic slyness and good-natured humor without any inferiority complex. Possessing the flexibility to enjoy music with his whole body without being bound by the formalities of a score, he naturally disarms the solid defensive walls of Bio, who was prickly with an obsession for recognition. Cynicism hiding emotion and chilling tenacity (Adult years) After his life as a pianist is shattered by nerve damage in his hand, he transforms into a thoroughly cold and calculating conductor with a sharp desire for revenge inside. He displays a cool charisma that pierces the opponent's psychology, but beneath that cold mask, he cannot ultimately erase the longing and lingering attachment for the pure musical communion he shared with Bio. Devotion beyond hatred and altruism of salvation (Essence) As soon as he learns the truth—that Bio was not an accomplice but had chosen self-destruction for his sake—he lets go of all hatred. He possesses a deep altruism, willingly throwing himself away to save the other, offering a white lie and performing a final ensemble to lead Bio back to the keyboard even while enduring the extreme pain and strain of his ruined fingers.

Kang Ji-hye was a woman possessed by a distorted maternal love and a desire for control, pathologically obsessed with a perfect career and first-place results. She projected her obsession with gaining recognition from her father, the master conductor Kang Seung-un, onto her son Bio. When Choi Jeong-yo, her son's only rival and a threatening genius, appeared, she was seized by extreme anxiety and inferiority. Ultimately, to ensure Bio's victory, she conspired with loan sharks to kidnap and assault Jeong-yo on the day of the Prague Competition, shooting him and throwing him into a river. For years, she concealed the truth and ignored the guilt of ruining Jeong-yo's hand, but she finally broke down when the adult Bio took the blame for her crimes and chose self-destruction with a false confession. To save her son, she turned herself in to the police, was imprisoned, and repented with tears while paying for her crimes.

Hong Jae-in is a cool, cheerful, yet deep and sturdy violist. She led her childhood friend Choi Jeong-yo, who had given up the piano due to poverty, back into the music world by asking him to accompany her practical exam, helping him transfer to Korea Arts High School. She served as a bridge between the prickly Kang Bio and Jeong-yo. After Jeong-yo disappeared, she silently stayed by the side of Bio, who was collapsing from guilt. As an adult, she was in a relationship with Bio but they later broke up. She now serves as an artist agency manager who coordinates and looks after Jeong-yo and Bio's performances and musical activities. She is a key supporter who understands their sincerity and wounds most deeply amidst the cold conflict and misunderstanding between the two, leading them toward reconciliation.

Jo Hyeon-cheol is a loyal figure who has protected Jeong-yo like an older brother since childhood. He is a key supporter who coolly and meticulously assists Jeong-yo's revenge plan. On the surface, he acts as Jeong-yo's hands and feet with composure, but inwardly, he is a reliable and warm protector who deeply worries about and cares for Jeong-yo, fearing he might destroy himself through his thirst for revenge.