Ch.1: Iori's boyfriend is sweet and very handsome, but the sex just isn't that good. That's why she has trouble maintaining romantic relationships. It's not like she's frigid or physically insensitive, either. After all, she has plenty of fun with her own vibrator. In fact sex toys are much more thrilling and way more pleasurable than sex with her boyfriend. That means Iori is spending her days troubled by a lack of good, intimate and pleasurable sex.
Cue: Her socially inept and hard-to-read little brother Aoi comes to her looking for some advice. "I can't seem to get my girlfriend off during sex." "What should I do to please a girl?" Here she thought this was going to be a normal brother-sister talk and out comes a totally unexpected romantic topic from her little brother. Thinking to play the role of big sis for once, she casually starts giving him advice but...

Official Translations:
English (DLsite, Coolmic), S.Chinese, T.Chinese, Korean

Ch.2: Iori had a problem: though the men were lining up to have sex with her, it never felt all that good. Then one day, due to a certain turn of events, she ended up in a sexual relationship with her little brother... And it was the best sex she'd ever had in her life. Better than all the men she had ever dated.

BUT... it was wrong. He was her brother after all.
Iori thus tries to find a new lover, and to put an end to their "innapropriate" relationship.

Little did she know... that they weren't actually related by blood.

Then the two of them take a trip to the beach with Iori's extrovert friends.
Unexpectedly, her brother begins acting possessively. When she is in the shower, he strips off her swimsuit and drowns her once more in the immoral pleasures of having sex with her "little brother."

Just when she thought she was out, he drags her back down into the depths of debauchery!

Official Translations:
English (DLsite, Coolmic), S.Chinese, T.Chinese, Korean

Ch.3: Iori had a problem: though the men were lining up to have sex with her, it never felt all that good. Then one day on an impulse, she began sleeping with her younger brother. And it was the best sex she'd had in her life.

It was wrong. Aoi was her little brother, and she had to end the relationship.
She found herself a new lover and attempts to end things with Aoi... All the while, Iori had no idea that they weren't actually related by blood.

That's when talk of a family vacation springs up.
Iori sees it as a chance to return her sibling relationship with Aoi back to something normal, but......?

Official Translations:
English (DLsite, Coolmic), S.Chinese, T.Chinese, Korean

There is a TL and R18 version.