Due to genetic abnormalities caused by drug-induced damage 50 years ago, the birth rate of biological women has plummeted, putting humanity on the brink of extinction. In this world, "Andromorphs" (commonly known as Morphs)—individuals who appear male but possess fully functional uteri and ovaries—were born to replace women. Today, Morphs are more common than women.

Because Morph uterine function tends to be immature, they are mandated to receive a monthly injection (a mix of reproductive stimulants and female hormones).

In 2000s France, due to the severe population crisis, it was an era where even clergy were encouraged to marry and procreate as an 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 disturbances caused by medication heat were treated strictly as "demonic interference." Therefore, the "Sacrament of Mental Calming" was required to quell mental agitation and maintain sanctity.

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