Hakuei Ren is the first imperial princess of the Kou Empire and serves as a general of its Western Subjugation Army. She is the third child of Hakutoku Ren, the empire's first emperor, and his empress, Gyokuen Ren. After her father and two older brothers, Hakuyuu and Hakuren, were killed in a fire during a revolt when she was young, Hakuei and her only remaining brother, Hakuryuu, were adopted by their uncle, Koutoku Ren, who became the new emperor. Unbeknownst to Hakuei for a significant period, this fire was orchestrated by her own mother, Gyokuen. At some point, she was chosen as a King's Candidate by the magi Judar and successfully conquered a dungeon alongside her attendant, Seisyun Ri, obtaining the djinn Paimon as her metal vessel. This achievement led to her being appointed to the rank of general.

In terms of personality, Hakuei is defined by her kind, determined, and strongly principled nature. Unlike the typically aggressive expansionist reputation of the Kou Empire's military, she is a pacifist at heart who genuinely desires to unify the world under her nation’s banner through peaceful means and diplomacy, believing this is the only way to achieve lasting global peace and prosperity. She strives to avoid conflict and seeks to build understanding rather than to conquer through force. However, she is not a naive idealist; she displays remarkable courage and an unshakable will, even in the face of death, as demonstrated when she refused to fight a hostile group and willingly accepted a sword wound to prove her sincerity. This event left her with a lasting scar on her chin. The rukh, or life-energy, around her is described by the magi Aladdin as being so honest it was almost painful to witness. Despite her serious responsibilities, Hakuei maintains a positive demeanor, smiles often, and is known for her care and affection toward her comrades.

Hakuei’s primary motivation is to realize her noble ideal of a unified world without enmity or violence. She sees the Kou Empire as the instrument through which this righteous unification can be accomplished and works as a general to further this goal. Her role in the story evolves from being a capable and compassionate military leader of the Western Subjugation Army to becoming a key figure within the larger political and military struggles of the Kou Empire. She participates in significant campaigns, including the attempt to subjugate the Magnostadt region, where she fights alongside her siblings against powerful enemies. Later, her motivations become more personal as she is forced to reconcile her ideals with the dark truths of her family's past and the manipulations of the organization Al-Thamen.

Her most significant relationships are with her family members. She is exceptionally close to her younger brother, Hakuryuu, whom she helped raise and is deeply protective of, and his well-being remains one of her greatest personal concerns. The revelation of their mother's treachery and Hakuryuu's subsequent thirst for revenge places a heavy strain on her worldview and her relationship with him. With her stepbrothers, her dynamic varies; she holds admiration for Kouen Ren, the de facto leader of their generation, and shares a cooperative understanding with him, though her feelings are complicated by the fact that his branch of the family now holds higher status. She is also able to interact comfortably with Koumei and Kouha. She shares a close, trusting bond with her attendant Seisyun Ri, her first household member, and the two conquered Paimon's dungeon together.

Over the course of her development, Hakuei moves from a position of relative innocence regarding her family's dark history to a state of profound awareness and internal conflict. Initially presented as a straightforwardly benevolent general, she gradually learns the extent of her mother Gyokuen’s deception and the sinister influence of the Al-Thamen. This knowledge forces her to choose between her pacifist ideals and her loyalty to her brother, who is consumed by a path of revenge. She becomes more entangled in the empire's high-stakes political maneuvers, struggling to prevent a civil war and to find a path that honors her principles while navigating a reality filled with betrayal and corruption.

Regarding her notable abilities, Hakuei is a dungeon capturer and the master of Paimon, the Djinn of Maniacal Love and Chaos, who possesses wind-based powers. Her metal vessel takes the form of a flabellum, a type of ceremonial fan. While she possesses a relatively low amount of magoi, or life energy, she is a competent fighter with skill in swordsmanship and considerable leadership ability. When she uses Djinn Equip, summoning Paimon's power, she dons a suit of gold, pink, and white armor. Her weapon transforms into a trident-like shape, and she gains the ability to generate powerful whirlwinds and tornadoes for both attack and defense. Paimon is also a fecundity-type djinn capable of reproduction, which explains why Hakuei has over a hundred household members, many of whom are from the Kouga clan she peacefully integrated into the empire. This grants her a significant number of loyal and empowered followers, making her a formidable military asset. Outside of combat, her hobbies include sewing, while her cooking is notoriously terrible, having nearly poisoned her closest attendant and her brother on multiple occasions.