Sun Mi shares many features with her children, sharing the same brown hair and eye color. As a middle age woman she shows some lines on her face, mostly around her eyes. In the missing poster she is shown wearing a yellow cardigan and a black and white pinstripe shirt.
Not much of her personality has been shown, she was shown as being kind and loving towards her children before she disappeared, making sausages and cake for her children on their birthdays. Dedicating days to treating them. Jae Gu however considers her cruel and monstrous for leaving him and his siblings behind.
Before the events of the story, her husband died from an illness which led her to have a breakdown. She was unable to cope with being a single parent of three children and abandon them one day, leaving Jae Gu to raise them by himself. Jae Gu states he has been looking for her, for two years.