Heartwarming: this eldritch entity's origin story is doomed yuri!
On a more serious note, this story genuinely must have been such a challenge to write and I'm super impressed at how the mangaka pulled it off. Consider that we "knew" the ending of the story going in: Matori must survive to the present day, and the town must reach its current state of deprivation. This created a great deal of dramatic irony by instilling in the reader the belief that the heroes couldn't win this one, that Matori must live to commit many murders...
Then to turn it around and reveal a whole bunch more lore about the nature of the Birth-Monk, the water, and even Matori herself, to have her instead killed and reincarnated in a way that makes complete sense plot-wise? To catch the reader off-guard after telling us the ending? It's impressive. To work in such cramped conditions as a writer, and make it out unscathed...