Furyou ni Hamerarete Jusei Suru Kyonyuu Okaa-san THE ANIMATION

Based on the erotic game by Erectlip.

The town is ruled by delinquents. As for you and your mother who lived happily and modestly, the delinquent's leader Shin got his eyes on your family. Your family ties begin to collapse as your cheerful and gentle mother's desire awakes by the cunning tricks of Shin. The only thing you can do, is to watch powerless at the figure of your most important person being toyed as a plaything. Now the game of the family falls into depravity's hell begins.....

(Source: Visual Novel Database)