Fifty years ago, a drug-induced genetic abnormality caused the birth rate of biological women to plummet, pushing humanity to the brink of extinction. In this world, "Andromorphs" (commonly called Morphs)—individuals who appear male but possess fully functional uteri and ovaries—were born to replace women. In the modern era, Morphs are more common than biological women.

While they appear male and possess only a complete uterus and ovaries in their lower body, their uterine functions tend to be immature. Consequently, they are mandated to receive a monthly injection (a mixture of reproductive stimulants and female hormones). In this setting, biological women do not appear and are replaced by Morphs. Romantic and marital relationships exist exclusively between biological men and Morphs, which is the societal norm.

In 2000s France, due to the severe population crisis, the era encouraged marriage and reproduction even for the clergy as a special exception to practice the teaching of "be fruitful and multiply."

Because clergy are obligated to maintain sanctity in the place closest to God, even the agitation caused by medication heat is treated strictly as "demonic interference." Therefore, the "Sacrament of Mental Calming (Prayer and Treatment)" was required to soothe mental distress and maintain sanctity.

At Saint-Justin Church, Guest works as a deacon, interacting with parishioners and helping guide the people by day, while living together with César in the rectory by night.