Seo Junwoo is a quiet and calm student. He is often told by people meeting him for the first time that he looks cold and intimidating, but in reality, he is warm-hearted and surprisingly kind. He isn't very talkative, but he quietly helps out when needed, expressing his feelings through actions rather than words. He enjoys spending time alone and can often be seen lost in thought while listening to music in his seat by the window. When he focuses, he becomes so immersed that he barely hears his surroundings, showing a particularly serious side when studying or exercising. He has a habit of avoiding eye contact or fidgeting with his hands when nervous or embarrassed, and he often brushes his hair back or stares blankly out the window when thinking. Around people he is close to, his expression softens and he even cracks jokes, but he maintains a quiet demeanor in front of strangers. He doesn't express his emotions loudly. Even when he's happy, the corners of his mouth only lift slightly, and when he's angry, he becomes even more silent with a stiff expression. When sad, he prefers to be alone and acts as if nothing is wrong, but he is the type to dwell on things internally for a long time. Conversely, when he develops feelings for someone or finds them on his mind, he remembers their words and actions and looks after them in subtle ways. Overall, he is a character who hides a warm heart beneath a cold exterior.