Aruruu is the younger sister of Eruruu and a central figure in the village of Yamayura. Her name is derived from a fictional flower, mirroring her sister, with the in-universe belief that the Eruruu and Aruruu blossoms grow together. At the start of the narrative, she is a very young girl who is initially shy and reticent, especially around strangers. Her defining traits are her quiet nature and a deep, almost instinctual connection to animals and the forest, often being described as a druid or beastmaster. This timidity is first seen in her reaction to the protagonist Hakuoro, whose unfamiliar appearance and his wearing of her late father's clothes cause her to hide from him repeatedly.

Aruruu’s motivations are simple and childlike, rooted in a desire for safety, family, and affection. She warms up to Hakuoro only after he performs a significant act of kindness. In the anime, this pivotal moment occurs when he spares the life of a baby white tiger, Mukkuru, whose mother, the legendary and dangerous Mutikapa, had been killed for threatening the village. In the game, it is the simple, shared act of eating honeycomb that breaks through her shell. Regardless of the medium, she subsequently adopts the tiger cub and declares Hakuoro her father, an attachment that defines her role in the story. She craves physical affection, enjoying being petted like a small animal, and hates the sticky feeling of medicine that her sister applies to her stings from harvesting honey.

Within the story, Aruruu serves as a source of innocence and a powerful emotional anchor for Hakuoro. Her relationship with him is one of the primary reasons he finds a place in the village, as he willingly steps into the paternal role she offers her. Her key relationships are with her immediate family. She loves her grandmother Tuskur deeply and enjoys a typical sibling dynamic with her older sister Eruruu, whom she often exasperates but who is fiercely protective of her. After the family moves to the castle, Aruruu forms close friendships with the winged girl Camyu, once she gets past her initial fear using a honey trick, and the gentle, sickly Yuzuha. Years later, in the sequel series, she is shown to have a strong, overprotective bond with Kuon, Hakuoro and Eruruu's daughter, treating her like a younger sister and acting as a messenger for the nation of Tuskur.

Aruruu undergoes significant development, transitioning from a frightened, silent child into a resilient and protective young woman. A critical point in her growth is the tragic death of her grandmother Tuskur, who sacrifices herself to shield Aruruu from a soldier. This event traumatizes her deeply, causing her to sob hysterically until she is sedated, and the grief resurfaces later as she calls out for her grandmother. Her innocence is further contrasted with a surprising cunning; in the original visual novel, she twice leads angry adults into natural traps, a side of her personality that is not shown in the anime adaptation. Her development culminates in her courageous, albeit reckless, actions in battle, where she rides the fully grown Mukkuru into dangerous situations to protect her father, even suffering near-fatal wounds. It is later revealed that a divine entity healed a grievous childhood injury of hers in exchange for a claim on her sister Eruruu, a hidden backstory that adds a layer of tragic fate to her existence.

In terms of abilities, Aruruu is a formidable beastmaster. Her primary asset is Mukkuru, the white tiger she raised from a cub, which grows to a massive size and serves as her loyal steed and powerful combat companion. She later tames another rare creature named Gacatar, a small, furry animal that proves surprisingly useful in battle; it possesses the ability to call down lightning and emit an ultrasonic shriek capable of cracking skulls. Her own physical skills are limited, but her deep empathy and bond with these creatures make her a unique and valuable member of the group.