Background: Before Sako became a ghost, she was a normal girl in her late teens who lived a normal life, but she died due to a serious illness.

Physique & clothes: She has ghostly white skin, long black hair that covers her left eye, and a tall, slender body with somewhat big thighs. 
She is also dressed in a knee-length, long-sleeved, white dress.

Personally: She is portrayed as a mean, teasing, and mischievous person.
Despite that, she's also kind and sweet.