Leo is a marginalized college student — poor and bullied daily by Derek and his gang. He has secretly loved Chloe, the campus beauty, for three years but never dared to speak to her. One day, Derek pushes Leo off the rooftop, killing him. But his soul slips into a tiny emerald-green snake, which happens to land in Chloe's backpack. Chloe finds the pitiful little snake, takes it home, and names it "Emerald." She keeps it by her bedside, changing clothes and bathing without hiding from it. Leo goes from despair to ecstasy — he has become his goddess's pet.
Derek pursues Chloe but is rejected. Enraged, he tries to assault her backstage at a dance. Leo goes frantic — his snake eyes turn golden, and a silent shriek sends Derek and his gang fleeing in agony. After that, Leo repeatedly uses his snake abilities to protect Chloe. During a camping trip, he drinks from a glowing moonlit spring and begins to mutate — growing a half-human, half-snake form. Finally, when a mysterious Shadow Organization attacks Chloe for her rare bloodline, Leo breaks all taboos. Before Chloe's eyes, he transforms from a tiny snake into a half-snake warrior, his face slowly revealing Leo's original features. Chloe recognizes those eyes: "You're... Leo?"
Leo ultimately fully transforms back into a human, retaining his snake superpowers. He crushes the Shadow Organization and rescues Chloe. The two kiss on the school rooftop, and Chloe says: "You're the best pet I've ever had... no, the best boyfriend."
