[SPOILERS] It's about a brother x sister relationship, the brother feels like he have to act as a father for his little sister, since their parents broke up, but he suddenly finds out that he's falling for her and attack her while she's sleeping, and that's why it's called Oyasumi Sex (Good Night Sex). Different it's what i can say about this one You know that incest thing were they make it clear that the sister it's actually a step-sister? Well i don't remember hearing that in this hentai, so well... thats different. Another point is that it shows both perspectives, the brother (who thinks he is doingsomething wrong), and the sister (who wants him to do it, but don't have the courage to say it).

It was good to watch but not too appealing, you might look for something else if you want more "action".