Luminus, whose full name is Luminous Valentine, is a central figure in the anime That Time I Got Reincarnated as a Slime: Visions of Coleus. She is a Demon Lord, holding the fifth seat of the Octagram, and is recognized as the true ruler of the Holy Empire Ruberios. As the queen of all vampires, she is among the oldest Demon Lords in existence, having lived for thousands of years. Her origins trace back to being created by the vampire progenitor Twilight Valentine, whom she eventually overthrew and killed using a powerful disintegration spell. Over time, she established a hidden vampire empire, first founding the city of Night Rose, which was later destroyed by the True Dragon Veldora. In response, she used the chaos of war among humans to create a new religion that reveres her as the one god, laying the foundation for the Holy Empire Ruberios and the Western Holy Church, which preaches the extermination of monsters while secretly serving her interests.

Luminus presents herself with a regal and composed demeanor, often appearing in a black gothic dress with a matching black ribbon in her silver hair. Her most distinctive features are her heterochromatic eyes—one crimson red and the other deep blue—and her pure white vampire fangs. Despite her youthful appearance, she is highly intelligent, cautious, and prefers to operate from the shadows, allowing her subordinates to manage public affairs. She is wary of humans and initially distrusts outsiders, as seen in her advice to Rimuru Tempest, though she ultimately respects his willingness to trust others. Beneath her dignified exterior, she possesses a playful and mischievous streak, occasionally enjoying theatrics and witty banter. She is genuinely protective of her loyal followers, such as the twin vampire brothers Louis and Roy Valentin, and has shown great care for Hinata Sakaguchi, healing her multiple times from mortal wounds.

In the Visions of Coleus arc, Luminus plays a pivotal role during the climax of the incident in the Kingdom of Coleus. The kingdom is embroiled in a succession crisis caused by Archdemons manipulating the royal family. When the Archdemons’ plans escalate, Luminus intervenes, arriving as a powerful external force to shift the power dynamics. She engages in a brief but intense confrontation with the Primordial Demon Violet (later known as Ultima), whose chaotic interference threatens the stability of the region. This confrontation highlights Luminus’s immense power and her vested interest in maintaining order among supernatural beings. Her involvement in the Coleus incident also establishes a foundation for her later interest in Rimuru Tempest and his growing influence.

Luminus’s key relationships include her loyal servants Louis and Roy Valentin, who act as her body doubles and manage the Holy Empire’s front. She shares a complex bond with Hinata Sakaguchi, the leader of the Ten Great Saints, whom she respects and heals despite their initial conflict. Her interactions with other Demon Lords, such as Milim Nava and Ramiris, display a blend of respect and rivalry. Most notably, her relationship with Rimuru Tempest evolves from wary neutrality to a strategic alliance, as both recognize the mutual benefits of cooperation. She also holds a deep-seated rivalry with the Primordial Demon Violet, which surfaces during the Coleus arc.

Throughout the series, Luminus demonstrates significant character development. From a hidden ruler content to manipulate human affairs through religion, she gradually becomes more willing to engage directly with the world’s shifting power structures. She adapts her strategies and alliances as necessary, showcasing her political savvy and long-term vision. Her growth is marked by her willingness to trust and cooperate with those she once considered threats, particularly Rimuru.

Luminus possesses formidable abilities befitting a true Demon Lord. Her Ultimate Skill is Lustful King Asmodeus, which grants her control over life and death. This skill encompasses techniques such as Re-Birth, which allows her to sense life energy and enhance regeneration to heal even mortal wounds, and Death Blessing, an instant-death effect that she can apply to targets. She is also highly skilled in powerful magic, particularly darkness manipulation, which she uses to devastating effect in combat. She can erect multiple defensive barriers, perceive magical energy over vast distances, and resist low-level abilities including mind manipulation, matter manipulation, time stop, and power nullification. As an ultimate skill user, her level cannot be appraised by those weaker than her. Additionally, she possesses superhuman physical characteristics, immortality, soul manipulation, and telepathy, making her an extremely versatile and dangerous opponent. Despite her reliance on dark magic, she remains one of the most capable Demon Lords, ranking as a Disaster-class threat.