Reiko Natsume, grandmother to Takashi Natsume, possessed the rare ability to see spirits, a power inherited by her grandson. Facing fear and ridicule during her youth due to this sight, she turned away from humans and sought companionship among spirits. To gain power over these entities, she challenged them to games; spirits who lost surrendered their names, which Reiko recorded in the "Book of Friends" she created. Though largely solitary, she did form a bond with a human classmate, Yorie Tsumura, who found her intimidating yet awe-inspiring. Reiko died young under unclear circumstances, fading from most human memory. She left the Book of Friends to Takashi, initiating his journey. Her legacy endures through the spirits bound within the book, including one who later took a human form (Mukuo) to comfort an elderly Yorie—fulfilling an old pact made by Reiko. Her motivations for collecting names remain ambiguous, with themes of loneliness and a search for connection, be it with spirits or humans like Yorie.