Seiko is tall, unlike Yuko, and has dark purple hair. Her hair is tied, and it seems to be wavy. She has black eyes and has fair skin. She usually wears a long sleeved white shirt over a purple sweater, and wears a purple long skirt.
When she was still a student in school, she closely resembled her youngest daughter in appearance according to her personal photo of her and Joshua.
She cares deeply for her daughters and tries to give them the best life despite being cursed with poverty. She is often shown saving money using loyalty discounts and cheap ingredients, to the point that the family has grown accustomed to it.
Seiko, like her two daughters, is generally kind. She speaks politely like Yuko and seems to be quite open minded.
- She stopped aging after becoming her husband's Vassal.