I wish this becomes a anime but not only 12 episodes like okamoto lynn other works
That anime would be too straightforwardly Hentai...too much risk for the studio involved.
There IS a reason why you do not mix sex scenes with meaningful story. The sexual part is too distracting, and sooner or later the whole story will just revolve around sex - which it does.
The only way this could happen would be a huge fan base, which I simply do not see. For example, on reddit,
Parallel Paradise has 2k members, whereas
Elfen Lied, another Okamoto manga, has 5.4k members. And Elfen Lied is like 20 years old and it is long over. I guess you can argue that elfen lied's popularity is (at least partly) thanks to the anime it got, but my point is that the parallel paradise community is way way too small.
... and Parallel Paradise isn't getting any more popular either, it has too little (->story) to offer for mainstream, non-hentai fans. So no huge fan base either. It's a shame really, because the story had several points, where it could have broken out from the "protagonist only have to mate to overcome an obstacle" mold. And it is obviously nearing its conclusion.