Based on the erotic game by Rune.

Will, an orphan originally from Little Monica, a city of culture and arts, returns to a place he hasn't been in since his childhood to contribute to it and have a reunion with his childhood friend, Celia. What he doesn't know is that during his long absence, things have changed for the worse and Little Monica, once a city of high culture has become a capital of degeneration. The question is can Will resist the temptations offered by the city or will he succumb to it. With a little help from Celia and her sisters Tina and Mei, as well Miss Meow, they just might succeed in returning Little Monica to its former glory.

(Source: Anime News Network)