Nao Iihara, cousin to Daisuke and Toruko, overcame frequent childhood hospitalizations stemming from health issues. She received care at a hospital where Daisuke's parents resided, and his consistent support during this period fostered her deep affection for him. Now fully recovered and healthy, she possesses a slim, pale physique with pink hair typically styled in a ponytail featuring shoulder-length strands and spiky bangs, alongside green tareme-shaped eyes. Her measurements are consistently noted as bust-waist-hips of 102-??-?? cm with a G-cup bust.

Her attire frequently includes school uniforms, nurse outfits, aprons without clothing underneath, Chinese dresses, and swimwear, reflecting her engagement in cosplay and role-playing. Personality-wise, Nao blends kindness, optimism, and a carefree spirit with stubbornness and a tendency to act at her own pace. Her clumsiness often requires intervention from figures like Mitsugu when her actions spiral out of control. She harbors persistent romantic feelings for Daisuke, openly pursuing physical intimacy and leveraging her understanding of his preferences to weaken his resistance. Pragmatically, she accepts his relationships with other women provided she perceives her share of attention as equitable.

In interactions, Nao displays a competitive and possessive streak, particularly when vying against rivals like Mitsugu Tsukushino for Daisuke's focus. This rivalry escalates to physical confrontations, including instances where she and Mitsugu restrain Daisuke to prove their desirability—actions that eventually provoke his rejection of belonging to anyone, straining their dynamic. Undeterred, she continues her pursuit.

Her background includes an unelaborated childhood promise with Daisuke. Across narratives, she transitions from high school to college. Her role-playing initiatives—posing as a nurse or wearing provocative outfits like a nude apron—highlight her direct approach to securing his affection.