Midori Mitsuya is an ace combat pilot assigned to the Rostock Corporation's March-Hare detachment. Her exceptional flying skills garner significant peer recognition. Upon fellow ace Yuuichi Kannami's arrival at the base, her direct curiosity and strong presence initially intimidate him.

She possesses an expressive and forthright personality, openly stating her thoughts without hesitation. This contrasts sharply with her profound internal struggle as a Kildren—a genetically engineered humanoid perpetually adolescent. She actively questions her existence, yearning for personal memories and horrified to find she possesses almost no authentic childhood recollections. Her memories dissolve the harder she tries to retain them, fueling deep uncertainty about whether her identity and few implanted memories are artificial constructs.

Driven by her longing for a genuine childhood, she hosts monthly parties at the base for all local children, attempting to imagine the normal growth experiences she never had. Despite this desire, she behaves with marked maturity, valuing adult conduct and expressing disdain for immature behavior, like that of pilot Naofumi Tokino. Her strongest resentment targets Suito Kusanagi, whom she views as failing her command responsibilities through self-destructive actions and childbirth—actions Mitsuya believes violate the role of a model leader.

Her storyline intensifies during a major Rostock operation. After heavy casualties and reinforcements arrive at Urisu base, she encounters a new pilot resembling deceased comrade Aizu Yudagawa, deepening her existential unease. She confronts Kannami, theorizing he is a reincarnation of former pilot Jinroh Kurita, deceived by implanted memories to maintain combat skill. This culminates in a psychological breakdown where she fires at Kusanagi, later stopped by Kannami. In this confrontation, Kusanagi confirms killing Jinroh at his request, prompting Mitsuya's further disillusionment.