Occupation/Background: The youngest son of Hansu Group and a detective in Violent Crimes Team 1 at Gangha Police Station. Investigation Style: Portrayed as a 'chaebol detective' who flips the script on cases by unhesitatingly using his immense wealth and connections. Season 2 Changes: Having returned after completing formal police academy training, he is described as having added investigative intuition and principles to his previous method of solving everything with money. Relationship with Ju Hyera: Ju Hyera was the harsh instructor who trained Jin Isu during his police academy days. In Season 2, she joins Gangha Police Station as the leader of Violent Crimes Team 1. Although their personalities and investigative styles clash, they are depicted as partners who complement each other in crises. Season 2 Premiere: The first episode centers on a tense scene involving a homemade bomb threat where Jin Isu identifies the bomb and Ju Hyera takes command to control the danger. In this process, Jin Isu acts under Ju Hyera's command, and the friction and cooperation between the two are highlighted as key points of interest.

A former ace of the National Police Agency's counter-terrorism team and the new leader of Gangha Station's Violent Crimes Team 1. To Jin Isu, she is the superior who was his 'devil instructor' at the police academy. In the first episode, she shows a strong presence with her cold judgment and charisma while taking control of a bomb site.

Introduced as a steadfast and righteous detective in Violent Crimes Team 1 and Jiwon's lover. In Season 1, he was the second-in-command of the team who closely assisted Lee Ganghyeon, and he is a character who initially clashed with Jin Isu but gradually grew closer to him.

Jin Myeongcheol (played by Jang Hyun-sung) Chairman of Hansu Group. With his innate insight and sharp mind, he bypassed several older brothers to take the chairman's seat at a young age. He currently oversees subsidiaries in electronics, logistics, pharmaceuticals, and chemicals. Having received an authoritarian and coercive education from his self-made father, Myeongcheol is a strict and blunt father to his children. He is polite to his subordinates but does not easily let people in, and he is a boss who coldly discards those he deems not 'his people.' His biggest headache is Isu. Isu has always wandered and caused trouble. Myeongcheol has reached a point of giving up on Isu, disappointed by his lack of interest in company affairs and his constant partying.

Isu's Secretary / Honorary Director of Hansu Group. A figure cherished by the previous chairman, he served as the CEO of Hansu Pharmaceuticals. Four years ago, when Jeonghun intended to retire, Myeongcheol asked him to look after the wandering Isu. Currently, he has postponed his retirement to stay by Isu's side. Like Batman's Alfred, Jeonghun takes care of everything and finds vast amounts of information; he is the person who knows Isu best in the world. No matter what trouble Isu gets into or what accidents he causes, Jeonghun protects and guards him. Perhaps Jeonghun is the father figure Isu truly desires. Thanks to that warmth, Isu has endured until now. A 'romance gray' who always carries humanities books and a dandy with a sophisticated sense of fashion.

Choi Gyeongjin (played by Kim Shin-bi) Member of Gangha Police Station's Violent Crimes Team 1. He is smart and has good instincts, but he doesn't think deeply. He works hard at assigned tasks but makes frequent mistakes and can be a bit clumsy. Whether he's oblivious or doing it on purpose, he says everything he wants to say. His work is somewhat hindered by flirting with his girlfriend of two years and liking celebrity feeds. Naturally, he is a follower of Isu. He has many interests, feels the need to express them all, and is faithful to his own desires. He truly hates it when work encroaches on his private life. He hates overtime and stakeouts. He is currently researching which department is the most idle. He was ready to bail at any moment, but since Isu joined the team, life has somehow become interesting.

Chief of Gangha Police Station. He has long forgotten his sense of duty as a police officer. He is petty and cowardly. With retirement approaching, he plays it safe even at the slightest breeze. He thinks it's best to gloss things over and close cases quietly, so Ganghyeon, who keeps escalating cases, is always a thorn in his side.

Leader of Gangha Police Station's Violent Crimes Team 2. Although he is far senior to Ganghyeon in terms of years of service, he is a perennial Inspector of 7 years. He hates seeing the much younger Ganghyeon racking up achievements. He torments Ganghyeon every chance he gets.