Well, that was bleak.
I didn't feel like there was enough change in the course of the story for it to really feel like a story. Obviously the ending brings release, and that's a change, but up until that, and in both that and other things the protagonist had no effect on anything. But that's a personal preference.
Why did the author choose to make the conjoined twins different sexes, I wonder? I don't think that usually happens, since they have the same genes, right? It even says that in the story. Was this meant to be thematically important somehow? Unless maybe they were genetically hermaphroditic and the way the conjoinment worked the sexes split between the two bodies? I don't know. Once I realized they were conjoined twins, I was trying to figure that out but I never came to any conclusion.