3rd generation chaebol, Gangha Police Station Violent Crimes Team 1 31 years old The youngest son of Hansu Group, possessing immense wealth and connections. He spent his 20s squandering his limitless potential just to have fun. After joining the Gangha Police Station's 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 'devil instructor' at the police academy who left I-soo with 'psycho' trauma! I-soo is determined to show her what a brilliant detective he has become, but he constantly finds himself falling behind her pace. It's a nightmare... Yet strangely, the two of them click perfectly. Despite their bickering, they join forces at every critical moment to overcome crises, becoming partners who create an odd synergy even in their discord. He speaks informally to everyone. He constantly makes a hand gesture called 'I-soo Peace' (crossing his index and middle fingers to form a gun shape). He occasionally suffers from 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 is persistent and meticulous, accurately grasping the core of a case. 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 gritted his teeth and pulled through without losing his spirit. He wasn't just a playboy chaebol. Working together in the violent crimes team, Hye-ra starts to take a liking to I-soo. Though he's full of bluff, reckless, and eccentric, he has the creativity to view cases from unique angles and the nerve to handle suspects like a sly snake. Most of all, he has the ability to clear blocked investigations with his enormous 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 be able to do it! She 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 man of principle, he used to clash frequently with the free-spirited I-soo, but they have now become trusted colleagues who can understand each other with just a glance. He recently started a secret relationship with Dr. Yoon from the NFS, and the world looks a bit different to him now.

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, unconditionally agreeing even with I-soo's most eccentric ideas. He always looks after the team members with a warm and kind heart.

Medical Examiner at the National Forensic Service 32 years old A sophisticated and talented medical examiner. Her only interest used to be corpses, but Park Jun-young eventually caught her eye. She seduced him by asking him out for meals and started dating him. But this man... has he never dated before? He's incredibly awkward. And that's also cute.