OVA
Description
Regina Dei 1000 Anni, known as Promesium, originated as the Millennial Queen dispatched from the planet La-Metal to Earth. Operating under the human alias Yukino Yayoi for nearly 1,000 years, she secretly oversaw Earth while working as a schoolteacher and assistant to astronomer Professor Amamori. Initially complicit in La-Metal's plans to invade Earth before a predicted planetary collision, she developed genuine affection for the planet and its inhabitants, particularly the professor's nephew Hajime. This bond caused her to question her loyalties and ultimately rebel against her homeworld's invasion, striving to protect Earth.

After these events, she returned to her homeworld, now called Planet Maetel or La Metalle, and ascended as its queen. Confronted with a dying artificial sun threatening extinction by freezing, she accepted scientist Hardgear's proposal to mechanize the population for survival. Undergoing the transformation first as a necessity, she mandated her people follow. However, this decision yielded unforeseen consequences as mechanization eroded humanity and free will. Hardgear exploited the situation to seize control, transforming the mechanized populace into instruments of his dominion. Promesium gradually realized her error as mechanical components spread across her body like lesions, signifying physical and spiritual corruption. Trapped in her mechanical form, she experienced profound regret yet could not reverse the process.

Her daughters, Maetel and Emeraldas, recognized Hardgear's manipulation and their mother's loss of autonomy. Refusing mechanization, they led a rebellion against the emerging Machine Empire. In a final act of humanity, Promesium aided their escape from the planet aboard the Galaxy Express 999, enabling them to warn other worlds of the mechanization threat. This act positioned her as the foundational figure of the Machine Empire, a ruler consumed by the very technology she embraced to save her civilization. Her legacy endured through her daughters' galactic journeys and their ongoing resistance against the mechanized forces she inadvertently unleashed.

Physically, Promesium possessed a tall, slender stature and long blonde hair, resembling her daughter Maetel, notably in her almond-shaped eyes across certain adaptations. Her transformation into the Machine Queen altered this appearance, with visible mechanical elements encroaching on her form. Her narrative explores themes of sacrifice, the erosion of humanity through technology, and the conflict between duty and personal conviction.