Nana Aihara is a supporting character in the anime Kimikiss Pure Rouge. She is the younger sister of Kazuki Aihara, one of the two male protagonists in the series. In the original visual novel, the protagonist had a younger sister named Nana, and this role was carried over into the anime adaptation as Kazuki's sibling. Nana is a high school student with short brown hair and brown eyes, and she typically wears her school uniform. She has a cheerful and somewhat mischievous personality, and she is often seen interacting with her brother and his circle of friends.

Nana's primary motivation is rooted in her close family ties, particularly her affectionate yet teasing relationship with her brother Kazuki. She enjoys being involved in the lives of those around her and adds a sense of warmth and everyday life to the story. One of her notable activities is forming the Udon Lovers' Association together with Narumi Satonaka, which highlights her playful and sociable nature. She is also known for carrying a small accessory in the shape of a green frog named Iwao, a quirky detail that adds to her character.

Her role in the story is that of a supporting figure who provides lighthearted moments and familial context. She does not drive the main romantic plotlines but instead serves as a source of comic relief and sibling dynamics. Over the course of the series, Nana remains largely consistent in her cheerful demeanor, though she occasionally shows a more thoughtful side when it comes to understanding her brother's feelings and the relationships of those around her. Her development is subtle, centered on her growing awareness of the complexities of love and friendship. She does not possess any special abilities; her significance lies in her interpersonal connections and the slice-of-life atmosphere she helps maintain.