A world where Spiria, a virus that causes delusions and hallucinations, has become an epidemic. The protagonist, Rui Genzaki, unfortunately gets infected with Spiria and begins to have hallucinations. His younger sister, Mone, takes him to Kamikawa Sanatorium Hospital. There he encounters his first love, Riza, the suspicious director, Anri, and strange monsters. Is the world you see reality? Or is it delusion?