Bennu is a significant character in the story, serving as the holy beast and familiar to the main protagonist. He is a phoenix, an ancient and powerful creature, though he spends most of his time in a small, unassuming form. In this diminutive state, he resembles a tiny, round chick with soft yellow feathers, a white belly, small brow feathers, and sharp, narrow eyes that belie his true nature. His stature is remarkably small, standing only about eight centimeters tall. When he chooses to reveal his true power, Bennu transforms into a majestic and enormous phoenix with resplendent golden plumage that radiates a fiery aura, gaining crimson feathers among his crests and becoming large enough to carry several passengers on his back.

Bennu's personality is marked by a sharp contrast between his outward behavior and his inner pain. He is a proud and foul-mouthed creature who is typically rude and does exactly as he pleases without hesitation. He dislikes being ordered around and is quick to insult anyone who annoys him, having been dismissive and rude even to his future mistress, Sariphi, upon their first encounter. This abrasive exterior, however, hides a deep and old wound. Over his very long life, which spans approximately ten thousand years, Bennu was repeatedly used by others for his incredible healing powers. He was taken for granted, and the cruel words and lack of gratitude from those he helped led him to become completely disillusioned with healing. In response to this mistreatment, he intentionally changed himself to his smaller, less impressive form so that no one would take him seriously and he would be left alone. Despite this transformation, the painful memories and harsh words still cut deep.

Sariphi is the central figure in Bennu's motivations and development. She is the only one who can understand his speech, and her sincere, kind-hearted nature and the genuine respect she shows him gradually restore the fire he had lost. Her unwavering faith in him, despite any doubts or naysayers, brings back his confidence and his willingness to help others. Although he would never openly admit it, he cares deeply for her. He primarily agrees to use his abilities for others because Sariphi asks him to or because she is in need. This bond fundamentally changes him, allowing him to move past the bitterness of his long history.

In the story, Bennu serves as a powerful ally and protector to Sariphi. After she successfully summons him, he initially consumes the food meant to help her regain her strength. Later, when an attack by assassins results in him being knocked from a high wall, Sariphi instinctively jumps after him. To save her, he transforms into his full phoenix form for the first time in a long while, catching her and flying her to safety, an act that astonishes all who witness it. This event solidifies his role as her familiar. His abilities are invaluable throughout the narrative. Beyond his transformation and flight, Bennu possesses potent regeneration powers, capable of healing flesh wounds, restoring blood loss, and mending broken bones. However, he cannot heal illnesses, such as seasickness. Through his contract as Sariphi's familiar, he also has a unique spiritual connection to her that allows him to sense her location no matter how far apart they are, a skill that proves crucial for finding her when she is in danger. He also enjoys simple pleasures, with a noted preference for peanuts and a hobby of drinking at night.