Why is it tagged twins?
Based on page 4, I'd guess they're at most cousins that looks identical to each other.

How many chapters are in total?

4 chapters in total, spanning 2 books.

So, basically "The sea, you, and the sun" again?

Now that I've re-read bits of that, it's quite similar. This one just has more SM elements and darker atmosphere I guess.

When there is more plot in a porn manga where the plot is... typically bad porn plot... I'd rather see the mangaka focus more on the porn side by having more pages dedicated to it. This is my problem with most of Mira's works. Too much bad plot, too little porn.

And here I thought that Mira is actually one of the more explicit yuri mangaka. I mean the doujinshi is laden with porn scene IMO, the back story I mentioned is about 2-3 pages in length. Now I'm curious, could you recommend some yuri manga that you find arousing?

I actually created an account just to comment about this doujin.

So I read the raws up till the end and I can say something about the ending.

It's a happy ending (kind of). Moe ends up with Ran after Ran realized that the dorm mother never really loved her, and it was Moe that could make her actually happy. There was also a back story about the basement, which turns out to be some kind of sex-ed class so the students don't get shocked by the real world when they graduated. The means might be rough but in the end everyone is actually happy and Moe became the new dorm mother with Ran being the new school chairman. There is some forced sex done though, but the one being raped doesn't seems to mind about it in the end

I understand this might not be for everyone, but I'm personally happy that Mira is trying new things.