Yoo Shi-jin is a captain in the South Korean Army's special forces. He is known for his charisma, bravery, and strong sense of justice. Shi-jin is often called "Big Boss" and leads the Alpha Squad. He is friendly and cool under fire, but struggles with honesty, especially when it comes to his feelings for Dr. Kang Mo-yeon. Despite the dangers of his job, he is dedicated to protecting his country and his team. Shi-jin is also known for his relentless pursuit of Mo-yeon, even when she tries to avoid him. His journey is filled with challenges, but his loyalty and determination shine through.