Master Liber

Age unknown (apparent age is 10), height: 146 cm, measurements: B 74/W 56/H 77. Former principal of the Royal Liber Academy and one of the "Great Demon Lords." Her specialized magic is Star Astrology (Summon Astrology). Her "Library" and 'Holy Ark' are Gluttony (Gula), and her "Theme" is Sanctity (Sanctus). Known as the "Arbiter of the Sacred (Sacer)," she is a part of the "Heavenly Arbiters." She is the leader of the Gospel Research Society (Ish-Kariote), and although her appearance is youthful, her manner of speaking is aged. Having lived since the time of the magical war that banished the Great Demon King Dies Trinity from the earth to the world of the Divine Gate, she is one of the oldest characters in the story.

She has mastered magic that borrows the power of evil gods said to exist at the ends of the world of stars, with her specialty being future prediction. Using this, she accurately deploys summoned evil god armies in battle to corner her enemies and extends her reach in schemes to achieve the desired future from countless possibilities.

She possesses an overwhelming ability to perceive loop phenomena that repeat infinitely without anyone's recognition, allowing her to be aware of events such as the repeated encounters between Arata and Ceres in the third volume of the novel and the fate of Liese being trapped in infinite time along with Chronos Trinity in the spin-off 'Liese Chronicle.'

She recognized Arata's potential as a Demon King from his childhood, when he showed no signs of awakening, and was the one who ordered Sei, who had parents affiliated with Liber Academy, to monitor and, if necessary, kill him. She aims to destroy this world by any means and create a world freed from the system of the Demon King, having various cards in her hand, including Sei, who was raised as an anti-Demon King weapon. Her "Sanctity" theme is due to her continuous research on breaking free from the system created by gods, worshiping and believing in evil gods.

Her true identity is one of the oldest active Arbiters, possessing the cunning of longevity and the ability to command evil god armies, holding the title of "Archbishop" as the leader of the Arbiters. Although her body and soul have deteriorated over time, her "existence" continues to maintain its identity over an immense period. It is revealed in the story that she was once close friends with Ceres during her lifetime, and her desire to not render Ceres's past sacrifice to seal the Great Demon King meaningless drives her activities as an Arbiter of the Demon King extermination faction. However, according to Amana, she seems to want to retire from the Arbiter's seat, and in the story, Akio is invited to the heavens as a successor candidate.

In the earthly world, she mainly connects to the "Library" for reasons such as conserving magic power, but when fighting seriously, she connects to the 'Holy Ark,' temporarily transforming into a beautiful woman of mature age. Although her combat method of summoning evil god armies does not change after transformation, she gains the ability to rewrite attributes at a super-high level, allowing her to completely nullify the opponent's magical attributes for a significant advantage. Even if she is not adept at direct combat, she possesses and utilizes many cards, such as enhancement magic for Lugh and anti-celestial special attack magic, boasting considerable strength overall.

In the new chapter, with the revival of the "Goddess of Deep Darkness" approaching, she moves her plan to the final stage, completing the anti-Demon King weapon "Black Emperor Flame Realm" using Sei as a sacrifice. She orchestrates a battle between Sei, who has become the embodiment of the Heavenly Emperor's ultimate law, and Arata, completing the steps for Arata, the embodiment of "Emotion," to be trapped and self-destruct in the Black Emperor Flame Realm upon Sei's defeat and disappearance. Afterward, she speaks of the extensive preparations made to reach this development among infinite possibilities and parts ways with the members of Biblia Academy, who were in a semi-allied state. However, when Faunalia and Maris, who visited the earthly world shortly after, insult Sei, she unusually reveals her anger and demonstrates her overwhelming power by defeating Faunalia. It seems she has her own affection for Sei and Lugh, whom she raised as her trump cards.