Hiromi Urino attends Kumashite High School in Tokyo, presenting as quiet and reserved with a stoic demeanor. She channels a contrasting expressive persona through a cat hand puppet, using it to voice blunt criticisms of teachers and the principal without personal attribution. Under the pseudonym "Mayuri," she regularly participates in the school radio program by submitting emails filled with mocking puns and wordplay targeting staff, contributing to a segment of imagined quotes. Her submissions frequently win phone strap prizes, amassing a collection of 28.

During broadcasts, she demonstrates dual communication: operating the cat puppet with one hand while texting messages with the other. This simultaneous expression occasionally requires her to physically suppress the puppet's unfiltered remarks to avoid disruption, citing an unclear reason—"no broken clutch system." Visually, she has yellow or light blonde pigtails, blue eyes, and rosy cheeks. Her social interactions consistently involve the puppet as a mediator, reflecting a separation between her reserved identity and the assertive persona channeled through it.