A student in Class 3-3 at the high school Arata transferred to. An upperclassman who sometimes comes to school in a boy's uniform and sometimes in a girl's, changing their first-person pronouns between "boku" and "watashi" accordingly. None of Arata's classmates know Mihaya's gender or background, and they are surrounded by various rumors, even being counted as one of the "Seven Mysteries" of the school.

A first-year high school boy. He is driven by an intense curiosity to verify everything from school legends and haunted spots to trivial rumors and even the taste of a cockroach. He transferred schools just to understand how a transfer student feels, and is curious enough to follow Mihaya Hayami into the restroom, if permitted, just to discover their gender. He is self-aware that his excessive curiosity is a chronic ailment.