Hello Monster — Characters & Cast

Initially seeks the truth behind his erased memories; evolves into an urgent mission to rescue his younger brother from the moral void.

Begins as an aloof, cynical profiler who treats human interactions as cold puzzles. As he recovers his childhood memories and reconnects with Ji-an and his brother, his defensive intellectual walls crumble, forcing him to accept guilt, vulnerability, and love.

Uncover the fate of her missing father and clear his name from suspected complicity with Lee Joon-young.

Starts as an obsessive detective branded as a "stalker" who relies on sheer persistence. She evolves into an emotionally mature investigator who prevents Hyun from falling into darkness while confronting her own unresolved grief over her father.

Longing to be remembered and sought after by his older brother, twisted into murderous attention-seeking.

Starts as a polished, chilling corporate attorney with an unsettling aura. Revealed to be Hyun’s lost brother, his journey shifts from calculated, resentful murder to heartbreaking vulnerability as he grapples with the truth that Hyun never deliberately abandoned him.

To prove his worldview right by nurturing Hyun and Min into mirror images of himself.

Appears in flashbacks as an enigmatic incarcerated killer, then in present day as a mild-mannered forensic medical examiner. His character maintains an unwavering, terrifying conviction that killing abusive adults and raising abandoned children is an act of salvation.

Prove his merit outside his powerful family’s shadow while keeping his quirky team intact.

Introduced as an insecure, privileged team leader trying to assert authority. Over time, he earns genuine leadership stripes, standing up against police corruption and protecting his unit.