Character Arc
Reiko Natsume is Takashi's late maternal grandmother and the original creator of the Book of Friends. Like her grandson, she could see yokai, but in her era this gift made her an outcast among humans who shunned and feared her. Lonely and rejected by people, she turned instead to the spirit world for company.
Rather than befriending yokai gently, the young Reiko challenged them to contests and games, and when she won she forced them to write their names in her register, binding them to her. This collection became the Book of Friends. Though her methods were domineering, many flashbacks suggest the bouts were as much about seeking connection as about power, since the spirits were often the only ones who would spend time with her.
Reiko died mysteriously before the series begins, so she appears only in flashbacks, memories and the recollections of the yokai who knew her. Strikingly, Takashi resembles her so closely that spirits frequently mistake him for Reiko. Through these fragments the audience pieces together a portrait of a defiant, solitary woman whose legacy of loneliness and longing for belonging Takashi inherits and ultimately redeems.