Nao Iihara is a main character in the adult anime series Boin and its sequel Resort Boin. She originates from a visual novel and is portrayed as a young woman with shoulder-length pink hair and green eyes. In Boin, she is a student at Kisaragi Academy, where she becomes involved with teacher Daisuke Ichijo through role-playing exercises intended to help students find suitable careers. In Resort Boin, she is a college student and a staff member at a resort, continuing her relationship with Daisuke.

Nao has a calm and easy-going personality, often described as cheerful and vibrant. Despite her relaxed demeanor, she can be somewhat naïve and is prone to jealousy, particularly regarding Daisuke’s interactions with other women. She shares a close friendship with Mitsugu Tsukushino, whom she frequently works alongside and competes with for Daisuke’s attention. While she is possessive at times, she is also remarkably open to sharing Daisuke with other partners as long as she receives equal affection. Her primary motivation is her strong romantic and physical attachment to Daisuke, which drives the central conflicts in her story.

As the series progresses, Nao becomes increasingly absorbed in her relationship with Daisuke, seeking more intense and unusual sexual experiences. This marks a shift from her initial role as a student exploring career options to a woman pursuing her own desires. Her notable abilities are not supernatural or extraordinary; instead, she is characterized by her emotional openness and willingness to adapt to new situations. Through her development, she evolves from a relatively innocent student into a more assertive partner who actively pursues her wants. Nao’s relationships with Daisuke and Mitsugu define much of her screen time, and her cheerful yet competitive nature makes her a central figure in both installments of the series.