Bong Do-jin: A fire suppression crew member and fire investigator known as the 'Bulldozer' for charging into flames. He is male and very cool. Dokgo Soon: The field commander of Taewon Fire Station, a motherly figure who cares for her team like her own children. Choi Ki-soo: A fire suppression member and the backbone of rescue operations, providing a silent and reliable presence on site. Ha Dong-woo: A paramedic and Song Seol's partner, assisting with emergency medical treatment on the scene. Gu Hyo-man: A fire suppression member who serves as the mood maker of the station. Song Seol: A paramedic at Taewon Fire Station known as 'Minnow,' a delicate soul who heals the hearts of her patients.

Jin Ho-gae: An inspector in the detective team, nicknamed 'Jindogae' (Jindo Dog) because he never lets go once he bites. He is male and close to the team. Baek Cham: The detective team leader. Though he's less sharp than in his prime, he remains a sturdy support for his team. Gong Myung-pil: Jin Ho-gae's dedicated partner. Despite his constant grumbling, he boasts the best chemistry with Ho-gae. Bong An-na: A sergeant in the CSI team and Bong Do-jin's younger sister, possessing sharp evidence analysis skills.

Kang Do-ha: The head of the forensic medicine team and an expert formerly from the Explosive Ordnance Disposal (EOD) unit. Yoon Hong: An NFS medical examiner in charge of the autopsy room, providing clues through cold and precise analysis. Shin Ae-ri: A forensic investigator who tracks traces on corpses alongside Yoon Hong. Han Se-jin: A commissioned forensic pathologist at the NFS who holds the key to a major plot twist.

Also known as MIU. Sleepground: Referred to as Inspector Sleepground. She is female and the central leader who guides the unit with excellent leadership and field command. Heugak: Referred to as Inspector Heugak. He is male and a machine/information security expert who analyzes high-tech equipment and systems. Soohyun: Referred to as Inspector Soohyun. He is male and in charge of psychological analysis and profiling, uncovering the hidden truths of cases. Rather: Referred to as Sergeant Rather. He is male and protects the team while securing scenes with powerful mobility and action. Coa: Referred to as Sergeant Coa. He is male and excels at summarizing clues and organizing data, handling initial investigation reports. Deokgae: Referred to as Corporal Deokgae. He is male and uses his 'sixth sense' to detect traces that are difficult to find through conventional investigation.