3rd Generation Chaebol, Gangha Police Station Violent Crimes Team 1 31 years old The youngest son of Hansoo Group, possessing immense wealth and connections. He spent his 20s squandering his limitless potential just to have fun. After joining the Gangha Station Violent Crimes Team by chance, he learned where to truly apply his power and abilities. Now, having completed formal police training, I-soo declares there is no case he can't solve. But then, Ju Hye-ra appears as the new team leader. She was the 'demon instructor' at the police academy who left I-soo with a 'psycho' trauma! I-soo resolves to show her just how brilliant a detective he is, but he constantly finds himself falling behind at her pace. It's a nightmare... Yet strangely, the two of them click. Despite their constant bickering, they join forces at every critical moment to overcome crises, becoming partners who create an odd synergy even in their discord. Speaks informally to everyone. Suffers from occasional trauma where his vision blurs and he has difficulty breathing. [Caused by the betrayal of the brother he trusted (who killed his biological mother) and the fact that he planted a bomb to kill him.]

Former Counter-Terrorism Team Leader at the National Police Agency, Current Leader of Gangha Police Station Violent Crimes Team 1 32 years old Sly and relaxed, yet a veteran with sharper investigative instincts than anyone. She pinpoints the core of a case accurately and is persistent and meticulous. Once called the ace of the Counter-Terrorism Team, she suddenly volunteers to be the new team leader at Gangha Station. She first met I-soo at the police academy as instructor and trainee. A 3rd generation chaebol as a cop? And a psycho at that? Interesting. She pushed him harder on purpose to see how long he'd last. But to her surprise, he endured and succeeded tenaciously without losing heart, even while grumbling. He wasn't just a playboy chaebol. Working together in the Violent Crimes Team, Hye-ra starts to like I-soo. He's boastful, reckless, and eccentric, but he has the creativity to see cases from unique perspectives and the nerve to handle suspects like a seasoned pro. Above all, he has the ability to clear blocked investigations with his massive funds and connections. Perhaps he is the essential person needed to catch 'that guy.' The one Hye-ra desperately wants to capture. With I-soo, she feels she might finally do it! Calls I-soo either 'Psycho' or 'Jin I-soo.'

Gangha Police Station Violent Crimes Team 1 31 years old A steadfast and righteous detective in the Violent Crimes Team. Being a principled person, he used to clash a lot with the free-spirited I-soo, but now they have become colleagues who trust each other enough to understand one another with just a glance. He recently started a secret relationship with Dr. Yoon from the NFS, making the world look a bit different lately.

Gangha Police Station Violent Crimes Team 1 28 years old The mascot and cute youngest member of the team. An 'MZ' detective with a sharp eye and great sense. He is I-soo's biggest fan, always agreeing with even his most eccentric ideas. He always looks after the team members warmly and affectionately.

Medical Examiner at the National Forensic Service (NFS) 32 years old A sophisticated and talented medical examiner. Her only interest used to be corpses, but before she knew it, Park Jun-young caught her eye. She seduced him into eating out and started dating. But this man... has he never dated before? He's incredibly awkward. And that's cute too.