Twisted Fates

Cha Hyunsu, now fused with his monstrous alter ego, awakens in the chaos of Hyosan High School's zombie outbreak. Driven by instinct and an alluring scent in the air, he finds himself drawn to the enigmatic figure of Yoon Gwinam, whose touch-starved souls craves the comfort and protection Hyunsu unknowingly provides. As their paths intertwine amidst the horrors of an apocalypse, a tender yet tumultuous bond forms between the almost feral Hyunsu and the bewildered Gwinam.

Or in other words...

Cha Hyunsu, who had just settled down to rest after escaping the military soldiers waiting for him outside his cocoon, wakes up in Hyosan High School's janitor closet during the initial outbreak of the zombie apocalypse in the school. He is perfectly hybridized with his monster ego, with it taking the backseat in operating his body, acting more like the base for his new instincts and personal soundboard rather than actively fighting him for control over his body anymore. So, when he catches a scent in the air that drives both him and his ego absolutely crazy, he doesn't fight him as his ego screams at him to go find whoever it belonged to and protect them with their life.