Onna no Miryoku

Sumire Senda is a housewife who wants to have sex with her husband right now. She has asked her husband to have sex with her many times at night, but he keeps refusing. As she continues to be turned down over and over again, she begins to wonder if she is no longer attractive. Then, while walking outside, she sees a suspicious poster. 'We can solve your sexual problems'. Despite the fact that she knew it was suspicious, Sumire went to the place indicated on the poster... There, Sumire receives a half-assed lesson on how to regain her charms...

(Source: pixiv)

Note: There is no NTR element in this story, as the ending is basically happy.