In Tokyo’s Shin-Okubo, Kai Fukudome (21) lives with his mother Yukie (53). On the way back from celebrating his mother’s birthday, while escorting his childhood friend Rika (21), Kai is suddenly attacked by a mysterious man.
Though Kai and Rika narrowly escape, tragedy strikes again days later: his best friend, Park Yujun (21)—a Korean resident in Japan—is killed by the same man. Soon after, both Yukie and Rika are also caught in the incident; Rika falls into a coma, and Yukie loses her life.

This shocking event reveals dark secrets: Yujun was actually a spy for Nation N, Kai has a long-lost twin brother, Lim Jin, a member of the mega-popular K-pop boy group Littlegang, and his estranged father Lim Dohyun (53), who abandoned him years ago, is still alive in Korea.

Kai’s fate shifts overnight… Determined to avenge his mother and best friend, and to uncover the truth about his own roots, he heads to Seoul alone. But what awaits him there…!?