Hana Oshiroi is a first-year high school student at Karasuma Private High School and a member of the Half-Priced Food Lovers Club. Small in stature with brown hair that she sometimes wears in a ponytail, she is almost always seen with her glasses and a bag carrying her laptop. Her name is derived from a flower, which appropriately symbolizes shyness and timidity.

At first glance, Hana appears quiet and reserved, a behavior stemming from a difficult past where she was frequently bullied by her peers. This experience left her with a deep-seated inferiority complex and a near-pathological fear of physical contact; she would often flinch and profusely apologize for getting germs on others if she accidentally touched them. However, this reserved exterior belies a remarkably excitable and vibrant inner world. Once she feels comfortable, especially around her friends in the club, she reveals herself to be lively, open-hearted, and surprisingly fearless despite her lack of physical strength.

Her central and most defining trait is her hobby as a writer of erotic yaoi novels, which she publishes online under the pen name Muscle Detective. She is constantly seeking inspiration for her stories, which feature thinly-veiled parodies of the bento brawlers she encounters, transforming them into overly muscular, sweaty men engaged in explicit scenarios. The protagonist of her novel is a clear analog of her clubmate, You Satou. Her fascination with muscles is all-consuming and often manifests in socially inappropriate ways. She can become flustered by a man's physique, obsess over the smell of sweat, and blurt out detailed muscle-related critiques, leading to her own frequent nosebleeds or causing her to act on impulses that border on harassment, such as massaging a surprised Satou without permission.

Hana's primary motivation for joining the violent supermarket battles is twofold: to secure a discounted bento for herself and to gather raw material for her next novel. Her role in the story is that of a non-combatant observer and chronicler. Unlike the other Wolves who engage in direct combat, Hana has no actual fighting ability. Instead, she employs a stealth-based tactic she calls the stealth rogue style. Using her small size and nimble movements, she waits for the other brawlers to become fully engaged in their fights before slipping through the chaos to snatch a bento and escape before anyone notices. Her success rate with this method is surprisingly high, showcasing a sharp intelligence and a keen sense of timing rather than brute force. In later battles, this ability to read the flow of combat sharpens to an extraordinary degree, allowing her to briefly foresee a few seconds into the future.

Her relationships are complex, particularly the one with Ume Shiraume, who has been her only friend since elementary school. Ume is obsessively and possessively in love with Hana, frequently kidnapping her, bathing with her, or interrupting her time with others. Hana finds Ume’s advances uncomfortable and overwhelming but remains loyal to her as her oldest friend. Within the Half-Priced Food Lovers Club, she forms a strong bond with You Satou and the club president, Sen Yarizui. Their acceptance of her as she is, without judgment, provides her with a sense of belonging and is instrumental in helping her overcome the trauma of her past bullying. She gradually stops apologizing for her very existence and becomes more at ease with herself. While she shows no romantic interest in Satou, she is keenly interested in his potential as a character in her novels, particularly his dynamic with the powerful brawler, Hana Nikaido.