Nanako Kanazawa emerges as an alternate personality of Kozue Aoba, manifesting during Kozue's moments of embarrassment or shock. She presents as a six-year-old child, exuding energetic, playful, and intensely curious behavior. Her visual traits include waist-length blue hair, yellow eyes, and a distinctive hairstyle featuring twin antenna-like ahoge often adorned with hair ribbons or bells.

This personality exhibits distinct childlike mannerisms, frequently engaging in imaginative play and displaying a short attention span. A notable behavioral shift occurs when she transitions into a "Shiny" state, becoming more subdued and better behaved. Among Kozue's alternate personalities, Nanako is uniquely defined by her specific apparent age, while the others lack explicit age indicators.

Her interactions within Narutaki-Sou reflect her youthful perspective, particularly her dynamic with Tamami Chanohata, who frequently documents Nanako's activities through photography. The surname "Kanazawa" incorporates the Japanese word for "gold," aligning with the series' theme of color-coded names.

The origin of Nanako and Kozue's other personalities stems from Kozue's childhood trauma. In the manga, they developed following her abandonment by parents and the death of her great-grandfather, with young Ryushi Shiratori's encouragement of imagination influencing their formation. The anime adaptation presents a different origin, attributing the personalities to Kozue's guilt over her parents' accidental death during a trip she gifted them.

Resolution comes through Ryushi's relationship with Kozue, leading to the integration of all alternate personalities into her core identity. The manga epilogue reveals Kozue and Ryushi later have four daughters, with one daughter physically resembling Nanako and embodying her youthful traits and mannerisms.