Itsuki Nakano is the fifth and youngest sister of the Nakano quintuplets, known for her serious demeanor, diligent nature, and notable appetite. Raised in a close-knit family, she remains deeply affected by her mother Rena Nakano's influence and passing, motivating her aspiration to become a teacher to honor that legacy. Academically, she excels in science and demonstrates strong observational skills, though she struggles with other subjects. She maintains disciplined study routines, including early waking habits and meticulously detailed work. Initially, Itsuki displays stubbornness and difficulty expressing her feelings honestly, especially during early interactions with Futaro Uesugi. She holds grudges, resisting his tutoring after their negative first encounter where he criticized her star-shaped hair accessories. This resistance gradually softens as she acknowledges her mistakes, accepts his guidance, and recognizes the necessity of academic improvement for her future goals. Her personality blends formality and politeness—consistently using honorific speech (keigo)—with relatable vulnerabilities like being a "crybaby" under stress, easily frightened, and naive about supernatural beliefs. A defining trait is her fervent passion for food, often seen consuming large meals or strategizing to sample her sisters' snacks. This gluttony leads to frequent diets and exercise regimens, accompanied by self-consciousness about her weight. Despite occasional food-related selfishness, she shows protectiveness toward her sisters, particularly Nino. She shares similarities with Nino like poor eyesight, morning exercise routines, and initial resistance to Futaro. Their bond features mutual support, with Nino often vocal in her defense. Itsuki's development includes forging key relationships outside her family. She becomes the first quintuplet to meet Futaro's family, forming an early connection with his sister Raiha during arcade visits and displaying natural caretaking instincts. Her dynamic with Futaro evolves into a trusted, non-romantic friendship marked by open communication. Though she realizes romantic feelings for him late—after his choice of another sister—she supports their relationship and focuses on her own growth. In later stories, including post-wedding specials, Itsuki actively pursues her teaching career. She navigates challenges like classroom management independently, demonstrating newfound self-reliance. During Futaro and Yotsuba's Hawaii honeymoon, she participates in a group effort to help a local girl, highlighting enduring teamwork with her sisters. Her career culminates in becoming a full-time teacher, fulfilling her dream while maintaining close familial ties. Itsuki's story arc emphasizes overcoming stubbornness, embracing emotional honesty, and achieving self-sufficiency. Her journey from an academically struggling student to a dedicated educator reflects her perseverance, while her relationships underscore her role as a unifying force within the quintuplets.