Read The Missing O hentai manga on hentaidexy.
summary for The Missing O :
Sex can be amazing, not to mention ecstasy inducingly mind-blowing. And Eunsung knows that because 7 years ago, she had good sex (an understatement). She felt the universe crack open to show her its secrets. Too bad she hasn’t had a decent orgasm since. It’s been a long journey, but everyone knows, before you get to “P,” you have to go through “O.”