Gyokuen Ren is a central antagonist in the narrative, known as the Empress Regnant of the Kou Empire. She is the widow of two previous emperors, having first been married to Emperor Hakutoku Ren, and later to his brother, Emperor Koutoku Ren. After the death of her second husband, she assumed the throne as the Third Empress of the Kou Empire. Her physical appearance is that of a slim, youthful woman of average height, noted for being a great beauty with a deceptively gentle and harmless look. She has short, dark blue hair styled with two long braids tied into loops, pale blue eyes, and a distinctive mole beneath her lower lip. She is typically seen wearing elaborate floor-length pink and white royal robes accompanied by a small hat adorned with a flower-shaped jewel.

The core of Gyokuen's identity is the revelation that she is not merely a human empress but is possessed by her own ancient ancestor, Arba. Arba was one of the three Magi from the destroyed world of Alma Torran and a former close ally of King Solomon, whom she ultimately betrayed. It is explained that Arba has survived for over a millennium by possessing the bodies of her own descendants, as she requires a blood relative to serve as a suitable vessel for her immense power. She took possession of Gyokuen after the birth of Gyokuen's first two sons, Hakuyuu and Hakuren. Consequently, the personality displayed throughout most of the story is that of Arba, not the original Gyokuen, whose true nature remains largely unknown.

In terms of personality, the being known as Gyokuen Ren is a master manipulator, characterized by her twisted, deceitful, cunning, and sinister nature. She is willing to commit any atrocity to achieve her goals, including orchestrating the deaths of her own children and husbands. The fire that killed the First Emperor, Hakutoku, along with her sons Hakuyuu and Hakuren, was an act of treachery she engineered to gain power. She is cold and ruthless, viewing her children merely as disposable tools or potential future vessels, a fact that drives her surviving son, Hakuryuu Ren, to despise her. While the original Gyokuen was remembered by her children as a gentle and loving mother, this behavior was erased after Arba's possession took full hold.

Motivated by a fanatical and ancient purpose, Gyokuen's actions are driven by her identity as Arba. She is the leader of Al-Thamen, a shadowy organization that spreads corruption and despair. Her ultimate goal is to resurrect the god Ill Ilah, whom she refers to as "father," in order to destroy the world created by Solomon and replace it with a void of pure black Rukh, free from the destiny imposed by Solomon's will. She believes her cause is righteous and shows no hesitation or mercy in pursuing the destruction of the existing world order.

Her role in the story is that of a hidden puppeteer who eventually steps onto the public stage as the Empress of the Kou Empire. She is responsible for allowing the distribution of Dungeons and Metal Vessels, as she does not consider them a threat to her own overwhelming power. She is the primary obstacle for her son, Hakuryuu, whose quest for revenge against her forms a major narrative thread. Her key relationships are therefore defined by her treachery. She is the hated mother of Hakuryuu and Hakuei Ren, the treacherous stepmother to the powerful brothers Kouen, Koumei, and Kouha Ren, and the mortal enemy of Aladdin, whose mother, Sheba, Arba killed in the previous world. Her possession of Gyokuen's body is a direct act of violation against her family, making all her relationships in the Kou Empire a lie built on a foundation of murder and betrayal.

Throughout the story, Gyokuen does not undergo development in the traditional sense, as her character is static in her fanatical devotion to her ancient plan. However, her arc involves the gradual revelation of her true nature and identity. Initially believed to be a benign empress, she is slowly exposed as the mastermind behind Al-Thamen and the tragedies of the Ren family. She finally reveals herself as the ancient Magi Arba and engages in direct combat with the heroes. Her development concludes with her physical death at the hands of her son, Hakuryuu, and the rogue Magi Judar. In her final moment, she smiles before her body self-destructs, and although that specific vessel is destroyed, her consciousness as Arba survives to continue her schemes by possessing another daughter, Hakuei Ren.

As for her abilities, Gyokuen is one of the most powerful beings in the setting. Being a Magi, she has access to near-limitless Rukh and Magoi, granting her incredible stamina and destructive power. She is highly proficient in manipulating Black Rukh and can even steal it from other users. Her defensive capabilities include a powerful Borg, a magical barrier that utilizes Black Rukh, which is strong enough to repel a full Djinn Equip attack. She can also expand this barrier offensively using a technique called Borg Al-Samm, which creates dragon-like heads to attack her opponents. Her offensive magic includes spells like Medoun Al-Samm, a destructive wave of energy that can severely injure powerful fighters like Hakuryuu and Judar. Beyond her magic, she is also an extraordinarily skilled swordswoman, claiming to have been the strongest swordsman in Alma Torran and having trained King Solomon himself. She wields a tall wand with a curved, jeweled head, which is actually the Divine Staff of Sheba, Aladdin's mother, which Arba stole after murdering her. Furthermore, as a pure consciousness, she possesses a form of immortality, allowing her to survive the destruction of her physical body and transfer her spirit to a new host, most effectively to her own biological descendants.