Lady Shimoni is a Yuki-onna. She appeared to be an underling of the queen of Snowy Night Village. At the end of Asagiri's flashback, she is turned into a ghost hag and dies. While she appears selfish and snobby at first, she shows worry when Asagiri agrees to become the sacrifice.
Shimoni (死娘) means "Corpse Girl" in Japanese. This most likely refers to how she was turned into a ghost hag.
Shimoni wears a basic yukata, covered in multiple patterns that appear to resemble flowers. Her hair is tied in a long loop held by a lily.