Ritsu Natsume is a 30-year-old Japanese government official within the Cabinet Secretariat's National Security Agency information team. She has short, straight black hair and grey eyes, typically dressed in professional attire like a tan business suit with a matching pencil skirt.

She attended university with Koujirou Shindou and Shuuhei Asano, forging lasting professional and personal ties to both. Her role involves intelligence gathering and analysis during national security crises. When the massive anisotropic cube "Kado" appears at Haneda Airport, Natsume immediately scours databases, identifying Shindou and Shun Hanamori as passengers on the affected flight. She subsequently participates in cabinet conference meetings addressing the incident.

Natsume holds romantic feelings for Shuuhei Asano, the Assistant Secretary for the National Public Safety Commission. However, she consciously steps back from pursuing a relationship, believing herself "not capable enough to handle him," adding a personal dimension to their government interactions.

Her responsibilities center on supporting the government's response to the anisotropic entity Yaha-kui zaShunina and its technological interventions. She participates in critical discussions and strategy sessions with the Prime Minister and other officials concerning these events. Across the series, films, and supplementary media like the OVA *Beyond Information*, her role remains consistently defined by her governmental position and her established connections to Shindou and Asano.