Himawari Furutani is a 13-year-old student with azure blue hair styled in two small front pigtails secured by a headband, gold eyes, and a notably developed physique for her age, including large breasts that cause recurring self-consciousness and teasing. Her name means "sunflower," recalling childhood accessories like sunflower hair clips. She lives directly across from Sakurako Ōmuro, enabling frequent interactions despite their contentious dynamic.

Her personality shows marked duality. Typically, she displays mature, polite, and lady-like behavior, using formal speech and demonstrating kindness, such as helping Chinatsu with knitting or preparing lunch with Yui Funami. She actively participates in the student council, aspiring to improve the school and later becoming a vice-presidential candidate. However, around Sakurako, her demeanor shifts to hostility and physical aggression, often berating or kicking her due to provocations—though this contrasts with underlying care, like assisting Sakurako with homework or sharing meals during a camping trip. This volatility stems from their childhood closeness, including a make-believe wedding orchestrated by Sakurako’s sister, Nadeshiko.

Academically capable but athletically challenged, she dreads physical education tests, a weakness Sakurako exploits. Paradoxically, her strength surges dramatically when angered by Sakurako, enabling feats like throwing her. She is skilled in domestic activities, including cooking meals for her younger sister Kaede and knitting. Body image is a significant concern; after mistakenly attributing changes to fat, she undertook extreme dieting until discovering it was breast growth. Sakurako and Kaede intervened, highlighting their latent concern.

Relationships define key aspects. She shares a devoted bond with Kaede, eating disliked foods to appear strong and covertly protecting her during errands. Her interactions with Sakurako blend rivalry with unresolved affection: they bicker constantly, yet moments like mutual blushing after contact, sharing wrapped cookies distinct from others, or Himawari covering a sleeping Sakurako with a blanket imply lingering attachment. Classmates like Akari and Chinatsu are casual friends, with Akari once commenting on her chest size. She also fears snakes.

Her background includes early academic dedication, joining the student council immediately upon entering middle school. Her established traits—conflicted affection for Sakurako, sisterly diligence, and body-related anxieties—persist throughout appearances in the main series, spin-offs like *Ōmuro-ke*, and other media.