Although the series offers only fragments, director commentary reveals Moonjo had a traumatic childhood, enduring abuse—particularly from his mother—resulting in facial scars which he hides under long sleeves .
According to those same insights:
• He killed his parents at a young age before being taken in by Ms. Eom, the landlady of Eden Dormitory, who may have enabled or encouraged his murderous tendencies.
• He grew up in an orphanage, a facility partially destroyed by fire—and its women’s section was burned down. Moonjo remains a somewhat mysterious figure, even within the drama’s canon .
Hence, his backstory loosely ties together trauma, adoption by Ms. Eom, and eventual descent into violence.