On Christmas Eve, the high‑schooler Ryouka Tsurumi awakes in her bedroom and discovers unsettling news. Her mother tells her that the family estate has been emptied and the surrounding zone sealed off because a mysterious, perilous presence known as X is in the area. The only other inhabitant left inside is Shuuhei Murosaka, Ryouka"s longtime friend. To deepen the terror, Ryouka learns that X can hypnotize people and feeds on human blood to propagate itself.
Shuuhei rushes in, rescuing her from one of X"s savage onslaughts. While the two friends attempt to flee the quarantined region, they are seized by mind‑controlled civilians and then eaten by the colossal creature. But Ryouka"s nightmare has only begun: she awakens a second time in her room, only to find that another X now endangers her. Realizing she is trapped in a repeating cycle, Ryouka decides to ally with Shuuhei and seek a future free from X"s menace.
The atmosphere of the mansion and silence amplify dread. Ryouka"s heart races as she realizes that each awakening may bring a incarnation of X, each more ruthless than the last.
