Reiko Natsume  

, 夏目 レイコ

Takashi Natsume's grandmother possessed a high level of spiritual energy, which granted her the ability to perceive and seal yokai. Despite being ostracized for her gift, Reiko created the Book of Friends as a means of finding companionship among spirits due to her loneliness. Since she believed humans could not comprehend her abilities, she turned to these supernatural beings for friendship. As an incredibly powerful individual, Reiko was able to compel spirits into following her commands through games; if they lost, she demanded their names and added them to the Book of Friends. This allowed her to summon any yokai whose name she possessed. An essential aspect of sealing involved Reiko's saliva and breath. Madara noted that she had poor table manners and was prone to forgetfulness. Regrettably, Reiko passed away at a young age, causing her contributions to be forgotten by many.