Michiko Kōzuki is a classmate of Mari Wakatake and Hagino Senkōji at the prestigious all-girls Kaihō Academy. She was born and raised in Kaiou City, where the school is located. Her family are local merchants, but they are not wealthy, nor do they belong to any of the prominent families that many of her peers come from. When she passed the entrance exam, her parents were overjoyed and stretched their finances to afford her tuition, a fact that weighs on her and shapes her personality. Because of her modest background, Michiko is naturally shy and reserved. She tends to keep to herself and spends more time helping the school caretaker, a man named Gen, tend the gardens than socializing with other students.

Her role in the story is that of a supportive and grounding friend. She is the first person to greet Mari when she arrives at the dormitory, and her gentle, unassuming nature helps put the troubled new student at ease. It is Michiko who encourages Mari to stay at the academy when she initially feels out of place, and their friendship becomes a steady, warm presence in the narrative. Michiko develops a close bond with both Mari and Hagino, though she remains largely unaware of the deeper, alien-related tensions unfolding around them. She is kind, loyal, and observant, but her timidness can make her hesitant in unfamiliar situations.

In terms of development, Michiko gradually becomes more confident through her interactions with Mari and Hagino, though she never takes center stage. Her modest means and lack of aristocratic background make her an outsider among the elite student body, yet she finds contentment in simple routines and her work in the gardens. She possesses no supernatural abilities; her strengths lie in her empathy, her quiet diligence, and her ability to offer emotional support to those around her.