Nino Nakano is the second oldest of the Nakano quintuplets, born on May 5th. She stands between 159 and 165 cm tall, initially possessing light pink to reddish-violet long hair which she later cuts to shoulder length, and has blue eyes. She typically wears twin butterfly-shaped ribbons and requires contact lenses due to poor eyesight. Her initial hostility toward Fuutarou Uesugi surpasses her sisters', marked by rebelliousness, sharp criticism, and active resistance to his tutoring, driven by protective instincts for her sisters and distrust of outsiders. Outwardly blunt and confrontational, she simultaneously displays strong maternal tendencies: cooking meals, baking cookies with decorative designs, managing medical needs including carrying band-aids for her accident-prone sister Yotsuba, and maintaining tidy living spaces with a distinctively girlish aesthetic in her room decor and fashion. She functions as the family's primary caregiver, a role complicated by occasional forgetfulness and fears of needles or ear piercing despite expressing interest in the latter before marriage. Academically, she ranks in the lower half among the quintuplets, with English as her strongest subject. Socially adept, she is described as a "social butterfly," skilled at making friends and maintaining networks, though sometimes oblivious to disguises or hidden identities. Her preferences include heavily sweetened black tea, customizable to her mood, and a fondness for romance films over documentaries.

Her character development starts with extreme antagonism toward Fuutarou, including an attempt to expel him using sleeping pills slipped into his drink. A turning point occurs on a school trip after she confronts her neglectful stepfather and Fuutarou retrieves her. Witnessing his determination and kindness triggers a profound shift in her feelings. She later cuts her long hair—a symbol of her resistance to change—signaling acceptance of her emotions and transformation. She becomes the most openly proactive sister in pursuing Fuutarou, confessing her love twice: first privately during the Kyoto school trip and later publicly in front of classmates, undeterred by potential rejection. This boldness contrasts her earlier hostility, though she retains traces of tsundere behavior, such as blunt denials of vulnerability. Her romantic awakening fosters maturity; she supports her sisters' ambitions despite rivalry, exemplified by encouraging Miku's culinary interests while maintaining her own childhood dream of opening a restaurant. Her protectiveness evolves to encompass Fuutarou, defending him against criticism and striving for his recognition. She files papers neatly, reflecting an organized mindset extending to relationships and goals. Interactions with her sisters reveal deep loyalty beneath frequent arguments, particularly with Ichika, whom she chastises for undermining Miku while still collaborating on schemes like coordinated Christmas gifts for Fuutarou. Her dynamic with Yotsuba involves caregiving for her injuries, and with Itsuki, she navigates typical sisterly disagreements. Though competitive in romance, she increasingly prioritizes familial unity and collective happiness over individual desires.