Fukutome Kai (21), who lives in Tokyo’s Shin-Ōkubo district with his mother, Yukie (53), is walking his childhood friend Rika (21) home after celebrating his mother’s birthday when they are suddenly attacked by a strange man. Kai and Rika barely manage to escape, but… Days later, Kai’s close friend, Korean resident Park Yujun (21), is killed by that same man. Not only Yujun, but Kai’s mother Yukie and Rika are also dragged into the incident—Rika ends up in a coma, and Yukie loses her life.

This tragedy leads to shocking revelations: Yujun had been a spy for country N, Kai has a long-lost twin brother—Im Jin, a member of the super-popular K-pop boy group Littlegang—and his estranged father, Im Dohyun (53), is living in Korea.

Overnight, Kai’s fate begins to shift dramatically. To avenge his mother and best friend, and to uncover the truth of his own roots, he sets out alone for Seoul. But what awaits Kai there…!?