When a swarm of giant bugs threaten to wipe out humanity, the world's only defense is a group of humans with special abilities called Butterflies. For Maehwa Baek, Butterflies are just heroic people he sees on TV, until a tragic event brings him to the scientists that created them. Soon, Maehwa must confront questions about himself that he has long avoided: why does he lose control at the sight of his own blood? And what happened during the period of 13 years in his life that he can't remember?