Nanako Amachi works as an investigator in Section Nine of the National Research Institute of Police Science. Her role involves navigating memory data extracted from the deceased via MRI technology to solve crimes. She possesses a subtle sixth sense that occasionally assists investigations by detecting emotional residues or concealed psychological states within the memory scans, though this ability remains low-key in her professional conduct.

Her character development unfolds primarily through interactions with colleague Ikkou Aoki, towards whom she harbors unspoken romantic feelings. This dynamic expresses itself through quiet concern for his well-being and discreet emotional support during cases. These feelings persist largely unaddressed due to Aoki's preoccupation with his duties and his complicated relationship with supervisor Tsuyoshi Maki.

A pivotal incident defining her character occurs when Nanako becomes a victim. After vanishing under mysterious circumstances, her brain is delivered to Section Nine for scanning while her body remains missing. This compels her colleagues to traverse her memories to locate her physical form and identify her abductor. Throughout this traumatic ordeal, her memories expose personal fears, vulnerabilities, and reflections on her relationships with team members.

The experience of having her own memories invasively scanned by colleagues generates ethical tension within the team and fundamentally alters her character. While specific long-term consequences remain undisclosed, this event highlights the personal risks inherent in Section Nine's work.