"Live outside." The boy's one word from six years ago endlessly circles in my head. *** Shim Seo Woo, who lived a normal college life, albeit with a somewhat clueless demeanor. One day, a chance accident awakens his spiritual eye, leading him to join 'Heun (痕),' an organization that hunts evil spirits. Heun, recognizing that Shim Seo Woo possesses the purification ability to cleanse evil, proposes that he work alongside Cheon Yi Jae, the organization's heir. "They must be desperate to attach a purifier to me. Seeing how they stubbornly found me and brought me here even after I said I didn't want to." Cheon Yi Jae, who harbors an evil spirit within his body, was an object of fear and vigilance for all members. Moreover, he keeps trying to kick out Shim Seo Woo, claiming he doesn't need purification... "You've lived a normal life, so why are you so eager to take on dangerous work? Can't you imagine? Your life could go wrong." "..." "Live outside." Cheon Yi Jae is always fierce and prickly, but his gaze keeps turning to him. "Have we met before?" And the more Shim Seo Woo sees Cheon Yi Jae, the more he recalls the boy he encountered in the past... *** "The boy I met back then... he's just like you."