Nanoka Kohinata is the fifteen-year-old female protagonist of Koi Kaze. She is a high school student who moves to Tokyo to live with her father and older brother, Koshiro, so that she can attend a school closer to their home. Because her parents divorced when she was young and she grew up living apart from her father and brother, she initially does not recognize Koshiro when they meet by chance before discovering their relationship. Nanoka is described as a bright, active, and cheerful girl who is largely typical of her age group. She is sweet and naive, enjoys cute things, and shares her interests with her two best friends. She becomes deeply attached to her brother after reconnecting with him, but is also easily annoyed by his brusque and distant demeanor.

Her motivations are rooted in a desire for connection and affection. She finds it natural to open up to Koshiro and is hurt when he reacts with anger or withdrawal. As the series progresses, she develops romantic feelings for him, a truth she initially hides from others and even from herself, though her friends tease her about having a brother complex. Nanoka is the first of the two siblings to consciously acknowledge the nature of her feelings, and she comes to terms with them before Koshiro does. Her role in the story is central to the exploration of forbidden love and its emotional consequences. She is empathetic and sensitive, often trying to understand and support Koshiro even as they both struggle with guilt and societal taboos.

Nanoka undergoes significant emotional development over the course of the narrative. She moves from innocence and confusion to a painful awareness of her own desires, and eventually to a deliberate acceptance of the relationship despite its complications. Her key relationship is with Koshiro, which drives the plot and her character arc. She also shares a bond with her father and maintains friendships that serve as a contrast to her inner turmoil. Nanoka possesses no supernatural abilities; her notable traits are her emotional openness, her capacity for empathy, and her courage in confronting her own heart.