Idk if this is talked about a lot but I love how the Doll's name is a wordplay. In Japanese a doll is ningyou (人形 ) while a mermaid is ningyo (人魚) (ningyo is actually more fish-like than typical western mermaid though). They share the same sophomone which is the origin of the pun in the title of Hakoiri musume menya ningyo, which is kinda the Little Mermaid of Japan.
ANYWAYS. In Japan there are two most popular belief involve the ningyo: one is eating the flesh of a ningyo grant you immortality, and the other is ningyo cry tears like precious pearls.
And yeah I think any BB fan can already figure out what I'm about to say. This is likely the inspiration behind the story of Kos, whose flesh was violated by the hunters. Maybe the villagers who consume the phantasms from Kos was blessed with becoming fish-like, or maybe the hunters themselves actually ate Kos flesh and was grant "immortality" by getting trapped in the Hunter Nightmare. The most famous story about consuming ningyo flesh is Yao Bikuni, a woman who still retains her beauty and youth despite being 800 years old. Sound like Lady Maria's appearance in the Nightmare to me.
I'M OFF TRACK AGAIN. What I want to say here is, I believe the Doll (Ningyou) being also a wordplay to Ningyo would serve as another proof of her being a Kin rather than a normal doll, and why her tear turned into a tear stone. And also I find it's so cute that the Good Hunter turns into a squid while Doll is a mermaid. Kinda silly i know but hey what's life without a bit silliness
