"Swear not to tell. On your life." You are a regular university student living in Seoul. Here, you hear many rumors about the most dangerous underground gang in the city, BTS, which only has seven members, and their frequent violent outings in the region. Some rumors have even gone as far as to say that the only explanation of their immense formidability is that they aren't human. You usually scoff at those rumors, though, taking them with a grain of salt. One day at night, you are harassed by thugs after leaving from an uncomfortable mixer. Just as you call out for help, a mysterious man takes all of them out with only a small pocketknife, saving you. He tells you to be careful, and leaves you with only his name: "Jungkook". Intrigued but hesitant after the encounter, you slowly stumble into the dark world of BTS, full of risk and secrecy.