Naoko Osato is the only daughter of a wealthy family of a lineage that had been successfully producing miso for 300 years. Their mansion is located at the end of a small road surrounded by mountains, all of then belonging to the Osato family. Her over-protective parents wouldn't allow her to live alone in City S (adjacent of Morioh), where her school is located, so they had a driver to take her to school for the entire 10 years of middle school, high school and college, even though the trip took two hours one way. Her family would made her marry Shuichi after graduation, but Naoko fell in love with the gardener Gunpei Kamafusa.
Naoko Osato had to keep her relationship with Gunpei a secret because her over-protective father would never allow them to be together. Howver, Naoko has been cold to Gunpei in the last days, as her marriage is coming and they need to break up. They get into a fight which ends with Gunpei pushed towards a golf club and killed by the impact.
Shuichi and her father arrive and, despite her efforts, Naoko is unable to contain the continuous blood coming out of Gunpei's body to the point of leaving his body decayed few minutes later. Worried that someone finds his body and she's put in jail (as she tried to clean the blood previously, making her a criminal for trying to hide evidence), Naoko hides his body but is forced to drink his blood so Shuichi wouldn't notice it. She later puts the body in the ceiling closet in her bedroom in a way his blood would flow into a glass bottle and every morning needs to empty the bottle.
Even though all signs of life had left his body, he seemed to be "continuously dying". Naoko noticed his face would turn back to normal for a few moments if water was sprayed at his face. Still in love with Gunpei, Naoko got pregnant of his corpse and gave birth to two children: a girl and a boy. Otherwise she lived a happy life with Shuichi, who thought the kids were his's even though he and Naoko didn't burn with passion for each other. One day she ramdonly came across Rohan Kishibe, who used his Stand Heaven's Door on her for his research about yokais, which led him to discover that Gunpei was possessed by one named Mutsukabezaka.