The protagonist Lin Yuan, 30 years old, codenamed "King of Hell", was once a top killer who made major organizations fearful. After getting tired of killing, he took on the ultimate mission - to protect the 5-year-old daughter of a deceased comrade and raise her up. From then on, the world's top killer disappeared from the market and became a full-time dad who tied his daughter's hair in pigtails and worried about her kindergarten homework.
