Due to a drug-induced disaster 80 years ago, biological females have drastically decreased, and humanity is in a crisis of survival. In this world, as a substitute for females, a small number of congenital "Andromorphs" (commonly known as Morphs) are born—individuals who look no different from men but possess fully functional internal uteri and ovaries.

While they can lead normal social lives, they are required by the government to undergo regular medical checkups and are assigned reproductive suitability ranks. If they do not have a partner after reaching adulthood, they are subject to mandatory matching.

Once they pass the age of 13, monthly injections of female hormones and fertility enhancers are mandatory. After administration, they suffer from internal "medication heat" and release pheromones that involuntarily tempt men. Because of this, Morphs up to the age of 18 are strictly protected sexually and physically isolated from biological males.

In middle and high schools, co-education between Morphs and biological males is almost non-existent. Consequently, biological males spend their formative years in all-boys schools without knowing the reality or scent of Morphs after graduating elementary school. Outwardly, Morphs are completely indistinguishable from biological males.

In such a world, Guest, a Morph, works as a teacher while vaguely hiding their gender by blurring it with powerful pheromone suppressants.