This is just my personal opinion on this manga.
Firstly, the art is great and the story is at the very least, thought-provoking. It was an interesting read.
But there were just some things that I felt were disturbing. While it might be understandable why Remilia would choose to forcefully transform Sakuya, it makes one question if you could really force someone you love to undergo that process, including chaining them to a bed for a full moon cycle (a month). At least the manga implies that Sakuya was barely conscious, though it would have been nice to see other residents of SDM at least stopping by to offer support in such difficult times. And the shock Sakuya got when she realized what her mistress had been doing to her...it's frightening to think how badly it can affect trust in a relationship.
But for Patchouli to justify turning Sakuya with "I need someone to bring me coffee every day"...
It feels a bit too flippant and apathetic, even for Patchouli. It's forcing someone close to you to compromise on their principles, and as evidenced later, sometimes a person's principles is what defines them and makes them feel worth.
We can see in the last chapter of this series that Sakuya sort of came to terms with her new state, but it would have been interesting to hear how she got to that point. We can see in the 3rd chapter in her conversation with Meiling that she is still unhappy about losing her mortality even after years have passed, despite her saying that she had forgotten how to be mortal. And suddenly the issue seems to have resolved itself.
Not to mention that throughout the series, most, if not all conflict or unresolved mental trauma is overcome by sex. It feels like the characters are relying on short-term reliefs to distract themselves from future problems that Patchouli seems to foresee at the end of the final chapter.
One thing the manga achieved is that it makes Sakuya suddenly feel "alien" to the reader. The first chapter provides insight into her inner thoughts and her expression changes to suit her emotion.
After transformation, the reader is no longer privy to her thoughts...and as Meiling observes in the 3rd chapter, she looks unhappy; she is virtually unreadable and barely cracks a smile outside of sex. She looks...hollow, and it felt sad.