Aoi, a childhood friend, has always been by Hiroto's side. Hiroto confesses his feelings to Aoi, and they start dating... Going to university together... Returning home together... They are living a smooth and happy life.

However, an ominous shadow looms over the two of them. A trending disease called "BFA-5" spreads throughout the country, and Aoi catches it. They decide to get her examined at a newly opened clinic in their neighborhood called "Gouyama Clinic." Thus begins the story of betrayal from that "examination"...