Mysterious beings called "Phantoms" have nearly eradicated humanity from Earth. Masashi, a compassionate and dependable adolescent, now resides with three companions; two teenage girls, timid Sanae and fearless Yaeko, and a young girl named Anna. Their harmonious coexistence gives them the impression that their fellow humans will return shortly, and they tend to their daily activities as if high school students after class. However, peculiar events begin to unravel, alerting them to the presence of the treacherous Phantoms. Can they disclose the truth behind the world's catastrophe?
