I really don't get it. If you're not willing to remove youmafication out of fear of the old oppression returning, how is subjecting everyone to the magic early onset dementia that turns you into a weapon of mass destruction better than erasing the distinction between humans and ninyou while also getting rid of youmafication? Either turn everyone into powerless humans or make all humans into ninyou. If the vessel's aramitama is so powerful as to be able to create the phenomenon of youmafication, why would the option of fixing whatever malfunction Cattleya is talking about while also removing youmafication not be a more obvious one?
Honestly, I don't know if the ax is to blame, but this feels like such a waste of a character that was at least somewhat intriguing in her motivations. It does feel like the author might have written themself into a corner by creating this hypercompetent and seemingly empathetic final boss that also had to clash with the MC at some point. How disappointing and stupid.