Hello Monster — Ending Explained

The central mystery unravels through overlapping layers of mistaken identities and buried memories:

• The Mother's Murder: Long before Hyun met Joon-young, an intruder broke into the Lee household and murdered Hyun and Min's mother. Young Hyun pulled out his father’s gun and shot the killer dead, but the intense weapon recoil knocked Hyun headfirst into the floor, causing severe head trauma and dissociative amnesia. Young Min hid and witnessed the carnage. The father covered up the homicide to protect Hyun, but misread Hyun's emotionless amnesia as born psychopathy, locking him in the basement.
• The True Identities: The genial Medical Examiner Dr. Lee Joon-ho is the fugitive serial killer Lee Joon-young, who took Min twenty years earlier. The calculating defense attorney Jung Sun-ho is young Lee Min, who grew up under Joon-young's tutelage, killing victims and sending puzzle cards to Hyun out of vengeful yearning.
• The Climax & Ending: When Min discovers Hyun never meant to abandon him, his thirst for vengeance shatters. Min visits Joon-young to end their toxic cycle and attempts to kill him, but is stabbed and left critically injured. Hyun rescues him. Joon-young disappears into an anonymous crowd, evading capture. Min recovers in hiding; Joon-young’s associate offers him a new falsified identity, but Hyun leaves the choice to Min: disappear into anonymity or pay for his crimes to live as his true brother. One year later, Hyun and Ji-an resume their lives and partnership, standing hand-in-hand as they continue tracking monsters.

Several distinct readings frame the series:

• The Psychological Tragedy Reading: This interpretation views the entire narrative as an indictment of Hyun’s father, Lee Joong-min. Had Joong-min understood his sons' trauma rather than labeling Hyun a "monster" based on Joon-young's manipulation, Hyun would not have repressed his memories, Min would not have been abandoned to Joon-young, and dozens of lives would have been saved.
• The Ambiguous Finale Reading: The ending leaves both Min’s future and Joon-young’s whereabouts unresolved. One view argues that Min chooses to atone and accept justice to remain Hyun’s true brother, while a darker reading suggests that Min remains incapable of fully integrating into moral society, leaving his decision perpetually suspended.
• Joon-young as a Distorted "Savior": Critics and viewers point out that Lee Joon-young genuinely perceived his murders as acts of altruism—killing abusive guardians to rescue abused children. The drama asks whether evil can emerge from a perverted form of empathy rather than pure sadism.