The year 2042. An era where Japan's economy has declined and a sense of apathy has spread even among children. When Kanjo Leo, a student at Tokyo Metropolitan Shinjuku First High School, woke up, he found himself at the entrance of Kabukicho. The scenery was somewhat different from usual. It was a strange sight—the sun was up, yet there were no people around, and the shops were destroyed. As Leo stood there bewildered, Kiri-shima Sayoko, a girl from the same high school, appeared before him. "All the adults have disappeared from Shinjuku!" According to her, it's impossible to leave the Shinjuku area, which is surrounded by a fog. Inside this Shinjuku, only minors under the age of 18 remain. Daily necessities are periodically airdropped by drones, and there is someone behind this setup. To navigate through this situation, Leo seeks out his childhood friend, Koiwai Rinichi, and asks for his cooperation. With Rinichi, who never forgets the contents of a book once he's read it, and the physically strong, loyal Leo teaming up, they strive to survive this predicament—! Meanwhile, an adult watches their existence through surveillance cameras from the "real Shinjuku." That man's name is Nancy. The company he founded at a young age has grown into one of the world's leading IT enterprises, and people call him the "Media King." Why exactly is Nancy watching them? And can Leo and Rinichi survive—?