Hana Midorikawa serves as the secretary of the Underground Student Council, a vigilante organization within the school. She is a loyal subordinate and friend to Mari Kurihara, the council president. Hana is a highly skilled martial artist, holding the rank of third-degree black belt and recognized as the fourth-best karate champion in the inter-high school championships. Her role in the story evolves significantly; she debuts as a secondary antagonist enforcing the council's harsh discipline but later becomes an unlikely ally to the male protagonists before emerging as the primary antagonist in the final story arc.

Physically, Hana is a slightly short and lithe young woman with an athletic and somewhat muscular build, belying her light frame. She has blonde hair styled in a bob with blunt bangs that cover her eyebrows, and brown eyes. Her standard school uniform is typically worn with blue leggings and an undershirt, a practical choice that distinguishes her from her peers and allows for her powerful kicking attacks.

Hana’s personality is defined by a stark duality. The initial impression she gives is that of a kind, cheerful, and somewhat innocent individual who enjoys brewing and drinking dandelion tea and has a fondness for four-leaf clovers. However, this gentle exterior masks a violent temper; when angered, she expresses her fury with swift and proficient karate attacks. Despite her tough and authoritative persona while on guard duty, she is actually quite shy, impressionable, and easily mortified, especially when confronted with compromising or sexual situations, which can cause her to faint. She also harbors a peculiar fear of mushrooms, stemming from a past experience during a hospital visit.

Hana’s motivations are heavily driven by her sense of humiliation and her subsequent obsession with the male student Kiyoshi Fujino. Their complicated relationship begins after Kiyoshi accidentally witnesses her urinating in a forest. In an attempt to get even and force him to admit what he saw, she orders him to urinate in front of her, a plan that backfires spectacularly when she ends up being urinated on. This incident, and a series of other awkward and intimate encounters, fuels a relentless and escalating cycle of revenge attempts. Her feelings evolve from pure vengefulness into an unrequited romantic crush, particularly after she and Kiyoshi share their first kisses. This emotional turmoil places her in a constant state of conflict, torn between her desire for retribution and her growing, confusing affection for him.

Within the story, Hana’s key relationships are central to her development. Her bond with Mari Kurihara is one of fierce loyalty and deep admiration, having served as part of her guard corps. She feels a strong sense of protectiveness towards Mari, believing the president needs her. Her dynamic with Meiko Shiraki, the council vice-president, is a contrasting one; Hana is more reserved and wears extra layers compared to Meiko’s more direct and physical disciplinary style. The core of her development, however, revolves around Kiyoshi. What begins as a blackmail scheme and revenge plot transforms into a complex obsession that drives her actions for much of the series. In the final chapter, her inability to suppress her jealousy and possessive feelings leads her to sabotage the potential relationship between Kiyoshi and Chiyo Kurihara, cementing her role in the narrative’s conclusion.

Hana’s most notable ability is her exceptional proficiency in karate. Her skills include lightning-fast reflexes, impressive agility, and explosive striking power that allows her to easily subdue opponents much larger than herself. Beyond her physical prowess, she demonstrates a capacity for psychological manipulation, using intimidation and blackmail, such as threatening to show compromising photos of her kiss with Kiyoshi to his love interest, to achieve her goals. Her cunning is also shown in strategic ploys, like sending misleading text messages to control situations to her advantage.