For hearing-impaired university student Yuki Itose, silence has been a natural part of life since birth. Her world is small and isolated; she commutes to campus, interacts with her best friend Rin Fujishiro, and communicates through writing and text messages—a lifestyle that offers little to no change. One day, during her commute, Yuki meets fellow student Itsuomi Nagi, a multilingual travel enthusiast and friend of Rin. When Itsuomi learns of Yuki's condition, he takes it in stride, moving Yuki's heart. From this one simple gesture, Yuki and Itsuomi's lives start changing day by day as they let each other into their own worlds.

It has been 10 years since Heaven's Gate appeared in South America and Hell's Gate appeared in Japan, veiling the once familiar night sky with an oppressive skyscape. Their purposes unknown, these Gates are spaces in which the very laws of physics are ignored. With the appearance of the Gates emerged Contractors, who, in exchange for their humanity, are granted supernatural abilities. In the Japanese city surrounding Hell's Gate, Section 4 Chief Misaki Kirihara finds herself at odds with an infamous Contractor codenamed Hei. Called "Black Reaper" in the underground world, Hei, like his associates, undertakes missions for the mysterious and ruthless Syndicate while slowly peeling back the dark layers covering a nefarious plot that threatens the very existence of Contractors. From the mind of Tensai Okamura comes a sci-fi thriller taking the form of a subtle exposé on a war in which political positions and justice have no sway—a war waged exclusively in the shadows.