Michiru Kita, a timid girl with difficulty expressing her thoughts, discovers peculiar ring-shaped markings on the necks of her classmates, Chika Akatsuki and Shito Tachibana, who had survived a tragic incident half a year earlier. These mystical rings, visible only to Michiru, serve as harbingers of doom. Driven by the desire to alter their fates, Michiru attempts to intervene, only to realize that her classmates are entangled in a different, ominous pact carrying a steep price.