Reiko Azuma sports short, disheveled black hair and sharp, jagged teeth. Her distinctive swirly square glasses contribute to an Opaque Lenses trope, rarely revealing her eyes. She typically wears a pink dress layered over a pink and white underdress.

An ardent fascination with the occult and supernatural phenomena defines her personality, driving her actions and relationships. This obsession leads her to befriend Wakaba Himeji, a classmate ostracized for perceived curses and spiritual connections. Unlike others, Reiko does not fear Wakaba's abilities and actively seeks paranormal experiences through this friendship.

Reiko becomes Wakaba's close friend and ally, frequently joining supernatural investigations. Alongside Wakaba and the creature Pō-chan, she discovers Naoya Yuuki, another student plagued by spirits. A significant event involves Reiko being struck by a car, resulting in a near-death experience. Wakaba and Pō-chan enter the afterlife to rescue her, preventing her crossing over. During this ordeal, Amanas Don Pescatore, an entity ruling Oblivion, captures her. Amanas attempts to force her reincarnation as his servant or wife using water from the Reincarnation Fountain. Reiko resists his plans and, with Naoya's assistance, defeats Amanas while Pō-chan destroys his castle and minions. This event underscores her vulnerability despite her occult enthusiasm.

Reiko's eccentricity manifests in behaviors like prodding spirits for reactions, exemplified when she repeatedly pokes a ghost with a neckache, provoking irritation. Her role consistently centers on supporting Wakaba and engaging with supernatural elements.