A reference to Thanatos no Yuuwaku. Go and read that short story. You'll crack an important code about the running theme of this manga.
Holy hell, this is a brilliant recommendation. The God of Death/Temptation of Thanatos being the true form of the Town's Abyss gives a great framework to understand this story. Why Yuuko wanted to birth a son to die with, same for Yumiko, and now Reiji, etc. I feel much more connected to the running theme of this manga now, thanks!