Miya Misumi hails from Fuso, the sole daughter of a wealthy family whose emerging business was founded by her grandfather. Her rural upbringing occasionally casts her as a "countryside wealthy lady." When her magical powers manifested, her father secured a retired witch as her private tutor, ensuring comprehensive development. This rigorous training propelled her to become a top student at Sasebo Aviation Preparatory School, receiving direct instruction from a Navy commander.

Her personality blends pronounced haughtiness and pride with careful discipline. She openly disparages those she deems less skilled, frequently mocking classmate Hikari Karibuchi's below-average magical prowess. Despite this arrogance, she respects authority figures and harbors a potent ambition to excel as a witch, revealing underlying dedication.

During the 1944 volunteer selection exam for European deployment, Miya competed against Hikari. Confident in her superiority, she initially dismissed Hikari's efforts. However, her overconfidence during the storm-impacted exam led to a collision with Hikari due to low visibility, causing both to crash. Regaining consciousness clinging to rocks in rough seas, Miya was swept underwater. Hikari rescued her by skipping across the ocean surface with magic, an act witnessed by senior officers. Although neither completed the exam, Miya demonstrated gratitude by formally thanking Hikari, signaling a shift in her demeanor.

Subsequently deployed to Europe in 1945, Miya traveled under Vesna Mikovič's guidance. Together they encountered and destroyed a long-range reconnaissance Neuroi. Following this engagement, she was assigned to the newly formed 507th Joint Fighter Wing stationed in Suomus.