Okay, I did some more searching and apparently Kuro CUL has an official 3D model, which you can look at here:
CUL was a model designed for the show VOCALO Revolution, organized by Hiroto-P. Modifications are ONLY allowed in terms of improving the appearance or changing colors for personal use, however, she MUST not be modified into entirely different character nor are parts allowed to be used on other...
mikumikudance.fandom.com
It also says that her voice was VY1's in the past.
Her JP name is hard to pronounce... Kuro KARU.
I found out that 濡鴉 is pronounced Nure-garasu (wet + karasu/crow) but apparently means "black haired".
It even has its
own Wikipedia page!
It is a word that describes the color of a woman's wet hair. "Wet crow" is the COLOR's name. Specifically, it is black with a hint of blue.
Other forms include 烏羽色/Karasu-ba-iro (color of crow's wings) and 濡羽色/Nure-ba-iro (color of wet wings). They refer to jet black, basically.
These are her official MMD videos by Hiroto-P:
I found
a blog entry by Gobou-P that talks about CUL's past.
He talks about the 4 sisters but says "Wouldn't Kuro CUL be the 5th sister?"
風雪月花 (wind, snow, moon, flower) is pronounced "fuu ka setsu getsu" and is actually Chinese. The Japanese version is 花鳥風月 "ka chou fuu getsu" (flower, bird, wind, moon) according to Wikipedia. It refers to the beauty of nature.
Found this tweet that said that CUL was initially to be the youngest sister of the 4 season girls.