Karen Clavius is the Military Ambassador from the Moon Kingdom (Kingdom of Sphere) to Earth. Holding the rank of commander, she leads a specialized military unit charged with safeguarding Princess Feena Fam Earthlight during the princess's residence on Earth. Her duties transcend formal protection; Karen also acts as Feena's trusted friend and advisor, providing steadfast support through diplomatic missions and personal difficulties.

Physically, Karen possesses aubergine-colored hair and green eyes, standing 1.66 meters tall with blood type A. As a lunar inhabitant, she exhibits enhanced physical capabilities—greater strength, speed, and agility—exceeding ordinary humans. She is noted for her high intelligence and academic dedication.

Her personality blends professionalism with genuine concern. While her military role demands strict discipline, she demonstrates warmth and deep loyalty within personal relationships. She maintains a long-standing friendship with Sayaka Hozumi, the United Nations president's primary secretary, originating from their university studies. Their demanding schedules limit frequent meetings, yet their bond endures.

Karen develops admiration for Tatsuya Asagiri, recognizing his kindness, bravery, and commitment to justice. She actively aids his endeavors, especially those supporting Feena's goal of Earth-Moon reconciliation. Despite her feelings, she respects his existing romantic attachments and refrains from interference.

Her role remains consistently focused as protector and supporter within the main narrative, contributing to diplomatic stability without central narrative focus, with no significant character evolution or expanded backstory documented across spin-offs or alternative media.