Kyungcheon, an aspiring pianist, finds himself in a peculiar predicament: he loses his heart and transforms into a milk cow. By day, he remains a man, but by night, he turns into a cow and grazes on grass. In a parallel storyline, a satellite named Ilho, dislodged from the cosmos by a supernova, is turned into a girl with the assistance of the wizard Merlin. One day, Kyungcheon is ambushed by a covert agency that targets individuals who have lost their hearts. With Ilho’s help, he manages to fend them off. After narrowly escaping the secret agents, the unlikely pair discovers each other’s hidden truths and grows closer.