Shinobu Ōmiya is a Japanese high school student characterized by straight dark olive-green hair styled in a loose bob and distinctive auburn eyes. She adorns the standard school uniform—top, vest, skirt, bow-tie, and shoes—typically paired with black tube socks and a black bolero jacket, switching to a light blue buttoned vest in summer. Her casual attire often features extravagant cosplay outfits regardless of the weather, though simpler feminine looks appear occasionally.

Her personality radiates extreme kindness, optimism, and a carefree outlook; anger surfaces rarely, primarily when she perceives threats to her cherished friendship with Alice Cartelet. Described as shameless and action-driven, Shinobu expresses feelings and pursues interests without hesitation. Alice perceives her as graceful and elegant, a perception contrasting with Shinobu's actual behavior. Academically below average, she struggles with focus but consistently supports friends with notable resilience. Her passions center on sewing and an intense fascination with Western culture, particularly blonde-haired individuals—later extending to blue hair after specific media exposure. She also possesses storytelling talent and exceptional hide-and-seek skills.

Shinobu's background includes a childhood homestay in England at age ten, where deep bonds formed with Alice Cartelet despite language barriers, culminating in a promise to reunite. Five years later, Alice moves to Japan, transferring to Shinobu's school and living with her family. This reunion integrates Alice into Shinobu's friend group, including childhood companions Yōko Inokuma and Aya Komichi. Karen Kujō, Alice's half-British friend, soon joins them, followed by Honoka Matsubara, who shares Shinobu's admiration for blonde hair.

Key relationships define Shinobu's world. She adores Alice Cartelet intensely, often fawning over her blonde hair while remaining oblivious to Alice's deeper feelings. Occasional conflicts arise from cultural exchanges or unintended insensitivity, swiftly resolved through mutual affection. Karen Kujō similarly captivates Shinobu due to her blonde hair, with Shinobu humorously suggesting she wouldn't mind a relationship with both. Yōko Inokuma, a friend since elementary school, shares Shinobu's academic struggles; their dynamic casts Yōko in a protective, sisterly role. Aya Komichi receives Shinobu's kindness but maintains a less intimate bond. Shinobu depends on her admired older sister, Isami Ōmiya, obeying her unless it conflicts with time spent with Alice. Honoka Matsubara bonds with Shinobu over their shared blonde hair fascination and appreciates Shinobu's sewing creations.

Character development revolves around Shinobu's dream of becoming an interpreter despite poor English skills and academic performance. Her sewing talent—creating intricate, noble-style dresses—prompts friends to suggest fashion design, but she prioritizes connecting cultures, inspired by her experience with Alice. Encouraged by Alice, she perseveres with English studies, eventually enrolling in a British university. Post-graduation manga sequels confirm significant language improvement, fulfilling her career goals.

Additional trivia includes her height of 155 cm, Gemini zodiac sign, and avoidance of technology due to beliefs like "catching computer viruses," explaining her lack of a cellphone. She cannot swim, fears hermit crabs from a childhood incident, and exhibits an age complex—distressed if perceived as old or very young. Her surname Ōmiya means "big shrine," while Shinobu means "endurance," reflecting her persistent nature.