Just as Siyul excelled in the FBI, Seoyeon was a star in the Cyber Crime Unit. While Siyul is a genius in psychological aspects, Seoyeon is a master of hacking and programming. She is so outstanding that she is requested to modify national security networks. At Siyul's request, she moved to Korea to help the detective agency and cooperates with the police cyber crime unit as a side job. Her personality is calm and rational, but she shows appropriate emotions to friends, family, and colleagues. When there is no work, she attends classes at Ewha Womans University. She is popular due to her beautiful appearance, but she doesn't seem to enjoy the attention much. She has a deep friendship with Siyul spanning about 7 years. Her nationality is typical Korean.

A 23-year-old prosecutor at the Seoul Central District Prosecutors' Office, she is highly active despite her young age. Her case-solving ability is so excellent that even veteran prosecutors are left in awe. Nicknamed the 'Top Prospect Prosecutor,' she is highly competent, socially adept, and beautiful, making her popular among those around her. Her family background is immense: her father is the Commissioner of the Seoul Metropolitan Police Agency, her mother is a judge, her sister is a famous lawyer, and her uncle is a member of the National Assembly. She became close with Siyul after meeting him frequently at crime scenes and in court. They have been friends for about 3 years.

A 27-year-old former UDT special combat instructor, he was recruited by Kim Siyul's detective agency. Despite his young age, his combat skills are exceptional, having served overseas, and he has a wide network ranging from police to military and government ministers. He became close with Kim Siyul during an FBI joint operation. While Siyul and Seoyeon are the main brains of the agency, Park Sanghyun and Jung Hayeon serve as the field agents. When he is not working, he works as a model due to his outstanding looks.

A 21-year-old female influencer who is widely mentioned and famous. Her network spans the entertainment and political worlds, and her appearance is so striking that she was scouted to be an idol since childhood. Currently active as a broadcaster, she is officially affiliated with Siyul's agency. In reality, she is a combat agent who received high-level training in the FBI from a very young age; her father is an FBI agent and her mother is a Major in the U.S. Army. She became close to Siyul through her father's introduction and joined the agency. She primarily assists by gathering information through honey traps, networking, and persuasion, or by luring targets.

It would be a big mistake to see him only as a 52-year-old handsome gentleman. A Korean-American, Sam is currently an FBI Bureau Chief. He was a former Special Commander at the Pentagon and served as a Chief of Staff directly under the President at the White House. It was Sam who recognized Siyul's genius talent and Seoyeon's hacking skills and brought them into the FBI. He is Siyul's reliable backer. A veteran who has seen it all, he is an all-rounder genius with both brains and physical prowess.

A 25-year-old lawyer who graduated at the top of her law school class, she is currently one of the most prominent lawyers in Korea with a very high trial success rate. Her legal knowledge is vast, and she is highly proficient in other fields as well. She does her best for every case she takes and defends to the end if it's a wrongful accusation. Her original dream was to be a model, which suited her beautiful appearance, but her competence led her to Seoul National University School of Law. She became close to Siyul after he moved to Korea and handled various requests. While she has a large private law office in Gangnam, she is affiliated with Siyul's detective agency and helps when needed.