Koyuki

is a pretty young woman who saved young Miroku's life seven years ago and died protecting children from the war.

History
Koyuki found Miroku lost in a snowy area seven years prior, and she saved his life.

During the story
Miroku encounters a woman who is identical to Koyuki and she takes him back to her home, because she claims that she has already birthed his child. Miroku is shocked to find many children living in her home, and he begins to take care of all of them.

Sango and the others eventually find where they have gone, and notice that the children Miroku has been caring for aren't children at all, but are balls of snow; they deduce that he must have had a spell put on him. Soon Inuyasha breaks into the home and Koyuki unleashes a snow beast on him; Inuyasha manages to momentarily get away from it and finds Miroku and snaps him out of the spell.

Miroku's friends work together to destroy the snow demon, and they free Koyuki's spirit from the demon in the process. It is revealed that Koyuki was the soul of a woman who had lost her life because of the war. After her death, she took in the spirits of children who also died in the war. At some point afterward, the snow demon took over her spirit.

Koyuki 小雪