The biological mother of Akatsuki Iride and the adoptive mother of Akira.

Spoiler

On the outside, she is a kind, normal mother and cares for her family deeply, but then after the death of her son, she adopts Akira (Akatsuki), but then her husband dies due to a laboratory accident and she loses her sanity, she becomes broken and pretends Akatsuki's a handmade doll. She was seen in Ichiya's flashbacks saying that he can only be normal around his broken sister, showing that she cares for him a lot. When Ichiya returns to the house, Yukako says that she's okay, since he had to take care of her all these years, so she's okay.

(Source: Naka no Hito Genome Wiki)