Story is about having yukkuris stimulated to give birth in their mammalian pregnancies early, resulting in a manjuu coming out, where they land on a conveyor belt to be taken away and sold. Due to the speed at which this happens, the parents are unable to form much of an emotional bond, and thus only die from overexertion.
There's a bit of explanation for this occurrence. In a mammalian pregnancy, the baby yukkuri is formed in a sac filled with paste, and it eats the paste around it to grow bigger before breaking through the shell like a chick. They then emerge through the mamumamu in a normal mammalian pregnancy.
There is a short scene of three children buying some of these eggs and betting on what type they belonged to, and one of them finds a mini yukkuri in the yolk.
The story ends with a baby Reimu emerging from one of the eggs left behind, and the writer wonders just what sort of world does it see, which is what the title is about.
The Scene Before Its Eyes, What Sort of World Is It?