The teacher is pretty sexy. I like the way she looks and how she acts. That's the good. So is the sister. I like the art style in this one and how the teacher is portrayed. Kept me watching until the end.
The male character doesn't speak a single word he entire show. You also don't ever see his face above his nose. It really took away from the story and what draws a person into it. Maybe there are episodes for a show before this that I haven't seen, since the description on this
site for the show says a bunch of past stuff that do not even get mentioned in this hentai. But, either way there isn't any real mention of that anything has happened previously.
The other girl (his sister I believe) has what seems like she has another being inside of her. Her voice changes with quotes around her dialogue in the subs and she starts to say/give what I interpret as "wisdom or advice," then she goes back to talking like a shy high school girl.
I am pretty sure there has to be a hentai before his that I haven't found mentioned anywhere in connection to this one. But, either way the fact that the male co-star (if you could really call a silent, hidden (no face) guy a silent character and the fact that it starts off with them having sex out of nowhere in a classroom where the teacher, at that time, keeps saying why is she doing this with a stranger" just makes no sense.
It is worth watching for the teacher who is damn sexy and has many great scenes where you get a good view of everything. But, they need to explain more, especially the part at the end with his sister (don't want to spoil anything). And if there is more info not in this from another show then they should have done some flashbacks or a quick recap, or even have the characters mention things during conversation.