Gate of Orgy: Lustful Training.

Maya, a housewife living an ordinary life, notices an obituary in the evening paper and reminisces about her past. Five years ago, her boyfriend died unexpectedly, and she lost hope in life. After wandering around, she ended up in Sagamihara, where she was captured by a thug who ran a prostitution ring. While being forced to take one customer after another in a prefab, Maya escapes from the guards and is taken in by a woman who calls herself "Osei." Osei runs an all-female group of compensated dating girls, but it is a world where strict rules must be followed to survive.