Nonoha Itō functions as a central supporting character across all three seasons of the Phi-Brain franchise. Her longstanding childhood friendship with protagonist Kaito Daimon involves preparing his meals and ensuring his school attendance, reflecting deep investment in his wellbeing. Though she consistently denies romantic feelings when questioned, her affection extends beyond friendship.

She possesses brown eyes and brown hair styled in a distinctive split ponytail. Her standard school uniform comprises a white t-shirt with a red ribbon collar, purple knee-length skirt, and pink sneakers. During the Sage Puzzle exploration, she layers a pink sweater over a darker pink shirt with maroon shorts.

Nonoha demonstrates exceptional athleticism and physical strength, frequently kicking Kaito airborne or applying headlocks when angered—particularly after he criticizes her confections. Despite most finding her cooking delicious, Kaito labels it "weapons of mass destruction," provoking immediate physical retaliation. Her recklessness surfaces when ignoring warnings about dangers within the lethal Sage Puzzle labyrinth.

Her cognitive abilities include a precise photographic memory, invaluable for recalling maze layouts and environmental details during puzzle challenges. However, she struggles with direct puzzle-solving, relying on unconventional tactics like maintaining wall contact to navigate—methods that sometimes lead to perilous situations requiring rescue. Her assistance proves crucial in Kaito's endeavors, such as identifying structural anomalies in dead ends or locating essential insignias to unlock paths.

After aiding kindergarten children during a puzzle incident, she unwillingly receives the Solver title "Nightingale," initially viewing it with embarrassment due to associating titled individuals with eccentricity. She exhibits protectiveness toward Kaito by stalking him when other females appear involved, often compelling their acquaintance Gammon Sakanoue to join these surveillance efforts. She makes tentative efforts to improve her puzzle-solving skills to better support Kaito, though this remains secondary to her established role.

Throughout the Solvers' global confrontations with the P.O.G. organization, she provides emotional grounding and practical assistance. She witnesses key events including Kaito's acquisition of the Orpheus armband, its evolution, and eventual shattering. No official media appearances beyond the primary anime series are documented, nor is information regarding family history, specific age progression, or post-series activities.