Midori serves as one of twelve guardian angels protecting Gorō Mutsumi. In her past life, she was a raccoon. Standing 140 cm (approximately 4 feet 7 inches) tall, she has brown hair and brown eyes. Her physical measurements show slight development across the series: B:71/W:58/H:73 in season one, shifting to B:74/W:58/H:74 in season two. Her image color is green, and her birthday is April 17.

Born on April 17, 1990, during her raccoon life, Midori encountered Gorō when he visited relatives in the countryside. He and his young cousin found the raccoon trapped while foraging in the mountains. They freed her, treated her wounds, and named her Midori. After recovery, she was released but soon died from food poisoning after eating wild poisonous mushrooms. This death instilled a lasting toxicophobia, making her a notably picky eater as a guardian angel.

Midori's personality is innocent and natural. She exhibits strong protective instincts toward Gorō, viewing him with familial affection as an older brother figure, differing from some other angels.

Her relationships evolve significantly. Initially, she clashes with Akane, particularly during an incident at a soba restaurant. Over time, however, they form a close bond, becoming best friends often seen together. Toki identifies both Midori and Akane as tomboys early on, though Midori adopts more traditionally feminine clothing in season two. Her friendship with Tamami becomes prominent in that season while they work together at the soba restaurant. Midori also displays a preference for soba noodles, observed in episode six.