Living with his mother Yukie (53) in Shin-Ōkubo, Tokyo, Kai Fukutome (21) is walking his childhood friend Rika (21) home after celebrating Yukie’s birthday when they are suddenly attacked by a stranger. Somehow, Kai and Rika manage to escape, but… A few days later, Kai’s best friend Park Yujun (21), a Korean resident in Japan, is murdered by the very same man.

The tragedy doesn’t end there—Yukie and Rika are also caught up in the incident, leaving Rika in a coma and Yukie dead.

In the aftermath, shocking truths come to light: Yujun had secretly been a spy for “Nation N,” Kai has an estranged twin brother—Im Jin, a superstar member of the mega-popular K-pop boy group Littlegang—and his father, Im Dohyun (53), who abandoned him long ago, is living in Korea.

Overnight, Kai’s fate is thrown into motion. To avenge his mother and best friend, and to uncover his own roots, he sets off alone for Seoul. But what awaits him there…!?