Hotarubi is a kunoichi, a female ninja, of the Iga Tsubagakure clan and is one of the ten warriors selected by the clan's elder, Ogen, to participate in the deadly conflict against the rival Kouga Manjidani clan. Her appearance is that of a slender young woman with straight, dark hair, embodying a classic image of traditional Japanese beauty. Her eyes are a deep purple color, and she typically wears a long purple kimono. Later in the story, she changes to a more practical combat outfit consisting of a purple kosode and hakama, with her hair tied back in a ponytail with a red ribbon. No matter her attire, she is almost always accompanied by a small white viper that coils around her neck, which serves as both a beloved pet and a deadly partner in battle.

Her personality is marked by a powerful duality. In public and among her clan allies, she presents a serious and no-nonsense demeanor. However, this front masks a much more volatile and passionate nature. Her primary motivation and the central focus of her existence is her love for Yashamaru, a fellow Iga ninja to whom she is engaged. Her devotion to him is absolute, and any perceived threat to his safety immediately shatters her calm exterior, unleashing a feral and uncontrollable rage. This is most vividly demonstrated when a Kouga ninja refuses to confirm whether Yashamaru is safe; Hotarubi flies into a frenzy, brutally stabbing him to death while screaming for an answer. Outside of these violent outbursts, especially when alone with Yashamaru, she can appear more innocent and even childlike, prone to jealous tantrums. She holds little respect for her clan's official heir, Oboro, whom she and most of the Iga consider weak and useless, instead deferring to the orders of the more pragmatic and ruthless leader, Tenzen Yakushiji. Some of this disdain may stem from a hint of jealousy, as Yashamaru once teasingly compared Oboro's sweet and feminine nature unfavorably to Hotarubi's more fiery personality.

Within the story, Hotarubi plays a significant role as a front-line combatant. Early in the war, she joins Tenzen and others in an ambush on the Kouga ninja Shougen Kazamachi, where her unique abilities are instrumental in securing victory. Following the mission, her primary goal becomes the search for her beloved Yashamaru, who has not yet returned from his own tasks. She uses her powers to send out scouts to find him, demonstrating how her personal motivations often intertwine with her duties. This personal quest becomes her entire reason for being after Yashamaru is murdered. When she learns of his death, her devotion to the war becomes absolute, driven by an all-consuming desire for revenge against the Kouga clan at any cost.

Her key relationships define her actions. Her bond with Yashamaru is the emotional core of her character, influencing nearly every decision she makes. She also interacts frequently with her fellow Iga warriors, particularly Nenki Mino, with whom she shares a pragmatic partnership in battle, and Tenzen, whose leadership she follows without question. Her loyalty to the Iga clan is secondary to her personal vendetta, and she shows little patience for those she considers weak.

Hotarubi undergoes a tragic but limited development. While she does not experience a fundamental change in personality, her motivations shift from protecting her loved one to avenging him. After Yashamaru's death, her actions become even more ruthless and desperate, driven solely by the need to make the Kouga pay. This ultimately leads to her own demise when she is tricked by a Kouga ninja disguised as her dead lover, proving that her emotional attachment is the strength that empowers her as well as the vulnerability that destroys her.

Her notable abilities are tied to a form of insect magic. She can summon and control swarms of glowing pink butterflies, which serve to overwhelm and distract her opponents, creating openings for her to land a lethal strike with her tanto, or short blade. This technique is often accompanied by a barely audible chant. In addition to her butterflies, she maintains a spiritual link with her pet viper, which acts as a guardian and scout. The snake is fiercely protective of Hotarubi and notably aggressive towards anyone impersonating Yashamaru, even biting the disguised assassin before its owner realizes the deception. Her fighting style is a combination of this mystical distraction, her own speed and grace in close combat, and the deadly assistance of her serpent companion.