Seiko Ayase is a powerful spirit medium and the youthful-looking grandmother of Momo Ayase. Known for her uncouth yet caring nature, she helps others selflessly, even while teasing and maintaining a tough exterior. Seiko wields immense strength, speed, and intelligence, using her bat, "Nessie," and supernatural powers like spiritual awareness, barriers, and the Power of Words. Despite her pride, she supports her loved ones and follows the code of coexistence between the living and the dead.