Masukawa Karato, the son of a renowned biology professor, frequently becomes a test subject for his father's culinary experiments. During a hectic morning dash to school, Karato unknowingly ingests one of his father's creations. Soon after, he experiences a strange sensation, leading to a collapse at home. To his astonishment, a string-like entity emerges from his chest, transforming into a captivating young girl. Declaring Karato as her rightful host, she sets out to safeguard and nurture him.