Kakeru lost his older sister five years ago. He tries to get back to normal life, but he still lives a vacant life. He has a childhood friend, Yuka, who goes to the same high school. She always tries to cheer him up and he gradually gets better.
One day all of a sudden, the sky turns red and the moon becomes black. Everyone besides Kakeru and Yuka disappears and monsters start roaming the streets. All they can do is just to run away and hide. A while later, it all gets back to normal. But when they start to think its all passed the Red Night happens again. They find out that there are four more humans who get involved in this mysterious phenomenon. They get together and try to survive, but six shadows appear in front of them...