Natsuyo Katsuragi is an elderly woman running a traditional Japanese ryokan deep in a snowbound, remote region. When a bus becomes stranded in a severe blizzard, she rescues its passengers, including protagonists Naoto and Miyuki, offering them shelter. She personally tends to Naoto after he falls ill. Her daughter, Yuki, assists her in managing the hotel and caring for the guests.

Initially appearing kind and hospitable, Natsuyo provides refuge as blocked roads and severed communication lines trap the group. However, her ryokan becomes the setting for increasingly strange and erotic occurrences among the guests. While aware of these escalating events, her precise involvement or motivation remains undefined. The environment she oversees transforms into a closed space marked by ritualistic and bizarre incidents, though her direct participation isn't explicitly detailed.