Based on the erotic game by Orcsoft.

On the 2nd anniversary of the marriage, Takahiko realizes that he is no longer getting sexually excited with his beloved wife, Manami. He is aware that this impotence is because of the strange custom he witnessed in his hometown, where a naughty feast takes place every night in the dark throughout the summer festival.
Long ago, he ran out of his hometown, horrified, but now he realizes that he can cure himself only by going back to that place...

Beloved young wife and the beautiful step mother he adores, pant in the pleasure given by someone else! The lewd netori festival of night begins...

(Source: DLsite English)