
When Ryoka, a high school girl, wakes up, she is left behind in a sealed-off apartment. A message from her mother tells her that there is a mysterious creature called "X" in the apartment.
When Ryoka, a high school girl, wakes up, she is left behind in a sealed-off apartment. A message from her mother tells her that there is a mysterious creature called "X" in the apartment.
When Ryoka hears that her childhood friend Shuhei is also left behind in the apartment, she calls him. What is the ecology of "X" that her mother told Ryoka as she waits for Shuhei to join them?