Doing

She has silver hair and pale blue eyes. She wears a lilac dress with a black coat, high black stockings and flat shoes.

Skills and Powers
Her power lies in tracking and spying through water. However, this power only takes effect if Yin is in the presence of water. Huang mentions that her "program" prevents her from showing any emotions or even making decisions on her own. However, this is later disproven, as Yin decides to stay by herself with Hei when given the chance to leave. Her real name is Kirsi, which is a short form of the Finnish name Kirsikka (meaning "cherry") or Christina, and she was a piano student of a famous Finnish pianist named Elis Kastinen (or Kostinen depending on the translation, both being Finnish surnames). Not much is known about her transformation into a "doll". Yin has a pale iris (possibly a cataract) that contributes to her partial or complete blindness. It is assumed that Yin has feelings for Hei, as when Amber appears before her she tells her that they look alike and asks her to take care of Hei.

Over the course of the series, Yin begins to show emotions and make decisions of his own free will, evolving over the course of the series.

In the OVAs during his transformation, his observer spirit developed an apparent form to his body and his own consciousness, becoming dangerous to control for the Syndicate and Hei himself.

According to a prediction from 50 years ago, it stated that a woman would awaken (in this case a doll) bringing a change to the world, in which it referred to that this doll would become Izanami, a weapon that would end all the Contractors in the world; I feel this prediction is true, since Yin was the possessor of Izanami, this being the awakened form of her observing spirit.