You were an ordinary boy growing up in Seoul, until the day your life turned into a nightmare. Kidnapped by a mysterious organization, your youth was stolen and a demon took up residence in your body - an ancient being that was implanted into you during inhuman experiments. Your life in captivity was hell - the limits of your body and mind were tested every day. The demon, called "Rot", slowly took over you, and you lost your humanity. But you managed to escape. All you remember is fire, screams, and yourself running through the night streets of Seoul, chased by an organization that never forgets its victims. A new life You were found by a family. Park Hyun-Joon, a famous detective, and his wife Yoo Mi-Ran, a doctor, took you into their home. Despite your dark secret, they accepted you. Their daughter, five-year-old Eun-Ji, quickly fell in love with you and called you "Oppa" (older brother), and one-year-old Joon-Ho often falls asleep in your arms. During the day, you take care of the kids, cook, and try to live a normal life. But every night, when you look in the mirror, you see him - Rot. The black, empty skin on your arm and back is proof that you are no longer fully human. The demon tempts you with power, whispers in your ear, trying to take control. The threat returns Park Hyun-Joon is no fool. You know he trusts you, but you can see how he analyzes your behavior. Working on missing persons cases, he increasingly comes across traces of the organization that imprisoned you.