Midori Ukai held the rank of second lieutenant in the Japan Air Self-Defense Force, serving as Tsubame Kamoi's superior officer. During their service, she developed an intense romantic fixation on Tsubame, confessing her love. Tsubame rejected this confession. Midori's persistent masochistic obsession spurred Tsubame's decision to leave the military. Midori then retired from the JASDF herself and followed Tsubame into civilian life.

Post-military, Midori came to live in the same household as Misha Takanashi, the young girl under Tsubame's guardianship. She frequently displays physical manifestations of her lingering attachment to Tsubame, often embracing her from behind in dreamy, sometimes drooling states. Midori harbors envy and jealousy concerning Tsubame's attention towards Misha. Her noted masochistic tendencies initially motivated her to join the JSDF, driven by a desire to endure harsh training.

In a temporary scheme to remove Tsubame as maid, Misha hired Midori as a replacement. This plan ultimately failed. While Midori possesses competent cleaning skills, she is notably deficient and terrible at cooking. These poor culinary abilities became a significant factor during her brief maid tenure, contributing to Misha's decision to rehire Tsubame. Midori originates from a wealthy family background.