Female. Early 20s. A young resident in the Emergency and Critical Care Medicine department at Yokohama Bay Hospital. Graduated at the top of her medical school class. She chose emergency medicine out of a desire to save every life. She has a sports-oriented, assertive personality, speaking her mind regardless of gender or seniority. While skilled, she is still inexperienced.

Male. Late 20s. The experienced ace ER doctor at Yokohama Bay Hospital. Believing that one must remain calm to save as many lives as possible, he is always composed and never shows emotion. While he is often strict with the impulsive Haruka Haruki, her presence leads him to rediscover his own mission as an ER doctor.

Male. Mid-20s. A paramedic (Emergency Medical Technician) at the Yokohama Minato Fire Station. Kind-hearted, responsible, and hardworking. He possesses a strong desire to save patients. Because he is not a doctor, he can only perform limited life-saving procedures, and he feels frustrated by the boundaries of his duties.

Male. Early 20s. A police officer in the Community Safety Department at Yokohama Minato Police Station. Currently assigned to a police box (koban). He has a strong aspiration to become a detective. He prides himself on his leadership, hates injustice, and cannot ignore people in trouble. A mood maker with a passionate heart who acts without regard for self-preservation.

Female. Late 40s. Owner of the cafe "Alloy," frequented by Haruka Haruki and Shozo Gonno. She is friendly and occasionally offers sharp retorts, but possesses an all-encompassing kindness. Rich in life experience, she warmly watches over Haruka and the other young professionals.

Female. Mid-50s. The head nurse of the Emergency and Critical Care Center at Yokohama Bay Hospital. Experienced, bright, and powerful. A motherly figure who serves as the emotional pillar for the nurses and doctors. She is strict but kind. She is the type to speak her mind bluntly without hesitation, showing no mercy even if the other party is a doctor.

Female. Mid-20s. A rookie nurse at the Yokohama Bay Hospital Emergency and Critical Care Center. She possesses a kindness that allows her to empathize with patients' hearts and a sincere desire to save them. A serious and dedicated individual.

Male. Late 40s. A Nurse Practitioner (NP) at the Yokohama Bay Hospital Emergency and Critical Care Center. He has a gentle personality and is excellent as a medical professional. With the reliable skills unique to an NP who can perform certain medical acts in collaboration with doctors, he supports the surgeries of Haruka Haruki and Subaru Kiryu.

Male. Early 40s. Director of the Emergency and Critical Care Center at Yokohama Bay Hospital. As a manager, he makes decisions while always keeping business conditions and legal risks in mind. He frequently clashes with the emotionally driven Haruka Haruki. Everything he does is to protect the ER center, but deep down, his desire to save lives remains strong.

Male. Early 60s. A veteran anesthesiologist who also works in the Emergency and Critical Care department at Yokohama Bay Hospital. He has worked at the hospital longer than anyone else, but he is not arrogant; he treats the young staff like his own children and interacts with them frankly. He is like a father to Haruka Haruki and a mentor to Subaru Kiryu.