Somewhere in Tokyo, hidden underground in a mixed-use building, lies a secret facility dedicated to training underground anal slaves for sexual release. Here, women with unique backgrounds are refined into perfect anal slaves to fulfill clients' desires. Training begins with anal masturbation and gradually intensifies to anal stretching and public enemas. As the regimen progresses, the women undergo physical and psychological transformation, becoming capable of enduring double penetration, bondage, and special anal play involving wax candles. To meet client expectations, extreme anal sessions push far beyond normal limits.