Tokiko Chida

Mamiya's older sister, who primarily appears in the past. She was hired by Ohtori Academy to oversee Professor Nemuro's work, and immediately has a significant impact on him. Her compassion for her brother provokes feelings that Nemuro has difficulty quantifying. She and Nemuro quickly bond over their desire to prolong Mamiya's life.

Her romantic involvement with Akio Ohtori is seen as a betrayal by Nemuro. Now he, in the present day as Mikage Souji, seeks to conquer his memory of her.