Synopsis：Unemployed bioengineering grad Lena Mercer reluctantly takes a high-paying underground lab job: feeding Subject Zero, an S-class lethal merman who has butchered 47 researchers over 17 years of captivity. Everyone else trembles at the mere sight of him—Lena shows up with instant noodles and small talk. The lab’s most feared man-eating monster is slowly “tamed” into a clingy, possessive creature who only opens up to her. When Zero finally breaks loose and drags her down into his secret ocean cave beneath the facility, Lena stands between him and armed forces aiming to erase him. In the end, she becomes his exclusive symbiosis researcher with triple pay, and the two slip into a quiet, lifelong co‑dependent existence deep below the surface, where no one else can reach them.