Ian's mother who disappeared when he was still a baby. Ian's father told him she looked just like a fairy. And Ian remembers how she held him and that she had green hair and red eyes, just like him.

Spoiler

Later, it's revealed that she wasn't holding him, but Tokage. She was a leannan-sidhe, otherwise known as a "muse". They seduce human men, and breath in the "foison". In exchange they inspire the man's art. This was the reason Kazumi was such a great novelist. However, doing this would eventually have killed the man. Kureha actually fell in love with her husband, and so left before she could kill him.

(source: wikipedia)