Yeon Si-eun is an intelligent, reserved, and observant Korean student. Although physically weak, he stands out for his strategic mind and strong sense of justice. He attends Eunjang High School but graduated and went to Seoul National University to take STEM as his course. He is introverted, analytical, and loyal. He struggles with expressing emotions. Si-eun has a slender, youthful appearance that makes him look physically weaker than many of the people around him. He has wide, doe brown eyes.