As the son of a famous biology professor, Masukawa Karato is often subjected to his father's experiments at the table. One day, while rushing to school, Karato accidentally consumes one of his father's sample dishes. Not long after, he begins to feel uneasy and ultimately collapses when he gets home. His chest expands, and a bundle of string suddenly erupts from it, quickly taking the form of a young, beautiful girl. Proclaiming Karato as her host, she begins her mission of protecting and caring for Karato.