Haru Miura is a student at the prestigious Midori Middle School who becomes deeply infatuated with the protagonist, Tsunayoshi Sawada. She is of a slender and short build. Her hair, which is black in the original manga but often depicted as dark brown in the anime, is almost always tied up in a ponytail with distinctive green hair bobbles. Her most commonly seen outfit is her school uniform, which consists of a white shirt, a cream sweater-vest with a blue bow, a gray pleated skirt, and black knee-high socks, though she is also known for constantly changing into a wide variety of costumes and disguises.

Haru is defined by her extremely upbeat, enthusiastic, and somewhat airheaded personality. She is fearless in her pursuits and often takes matters into her own hands, once even donning samurai armor and wielding a hockey stick to challenge Tsuna to a fight to test his worthiness as a Mafia boss. Her catchphrase is the exclamation Hahi, she often refers to herself in the third person, and she has a habit of ending her sentences with the polite suffix desu. While she is kind and caring, she is also notably more assertive than her friend Kyoko Sasagawa. When she believes Tsuna or his right-hand man Hayato Gokudera are acting immorally or foolishly, she does not hesitate to scold them sharply, sometimes even resorting to physical violence.

Her primary motivation and dream is to become the wife of a mafioso, a goal she develops after being rescued by Tsuna. Haru is fully aware that Tsuna is the boss of the Vongola Family, but she views this dangerous world through a romanticized, glamorous lens. Despite this fascination, she has a strong protective instinct towards children, particularly the young Lambo and I-Pin. She strongly dislikes the idea of children being involved in the mafia and is often the one charged with babysitting them. Another deep-seated aspiration, revealed to be from an elementary school essay, is her dream of becoming Japans best costume maker, which fuels her hobby of designing and wearing elaborate outfits.

Within the storys narrative, Haru serves as a recurring member of Tsunas inner circle, often participating in or being a direct catalyst for the chaotic events of daily life. During the serious Kokuyo and Varia arcs, her role is often to provide non-combat support, primarily by looking after Lambo and I-Pin. In the Future Arc, she is transported ten years into the future along with other non-combatants. There, her role becomes more crucial as she takes on domestic responsibilities like cooking and cleaning at the Vongola base. This arc also provides her with significant emotional development, as she is forced to confront the grim, violent reality of the mafia world she had romanticized. When Tsuna finally explains the true danger of their situation, she breaks down in tears, realizing her own previous selfishness in not understanding the seriousness of their struggle.

Harus key relationships are central to her character. Her closest friend is Kyoko Sasagawa, with whom she bonds over a shared love of cakes and often works alongside in domestic tasks. Together, they serve as a pillar of moral support for the group. Her relationship with Tsuna evolves from initial hatred, based on a misunderstanding, to deep adoration and a persistent, if often one-sided, romantic pursuit. She shares a friendly but argumentative rapport with Hayato Gokudera, often clashing with him while still functioning as part of the same team. She also has notable interactions with many other characters; fitting her love for costumes, she once considered Mukuro Rokudo a cosplay buddy, much to his dismay. She has an endearing habit of misremembering Chrome Dokuros name, calling her things like Cream Dokuro during her interview segments. She is also the one who named Hibari Kyoyas pet canary, Hibird, and she occasionally shows jealousy towards Uni because Tsuna blushes at the girl smile.

While Haru is not a fighter, she possesses several notable non-combat abilities. She has excellent gymnastic skills, being a member of her schools gymnastics club and using her agility to perform feats like climbing walls with ease. She is also highly proficient at sewing and can create detailed dolls and costumes. Her domestic skills are repeatedly highlighted, as she and Kyoko are both excellent at cooking and housework, making them vital to the groups daily survival. In video game adaptations, her Dying Will Flame is attributed as either Lightning or Cloud, but this is not part of the official manga or anime storyline.