Matsuoka Miu, a twelve-year-old sixth-grader, lives adjacent to the Itou household and habitually sneaks into their home via rooftop climbs and unannounced window entries. Her mischievous streak fuels surreal pranks and attention-grabbing stunts targeting peers like Sakuragi Matsuri and Ana Coppola, motivated by envy over their perceived charm and the favor they receive from Nobue Itou, Chika’s older sister.

Though long-time friends with Chika Itou, their rapport thrives on prickly exchanges, with Miu playing the cheeky instigator to Chika’s deadpan retorts. She needles others with boundary-pushing antics—mocking Ana’s name through deliberately unflattering kanji wordplay or fabricating absurd scenarios like feigning pregnancy after innocently sharing a bed with Nobue.

Her appearance is marked by chestnut twin pigtails tied with scarlet ribbons and brown eyes. She favors pink and red attire, notably a shirt declaring "I Am Boss," and owns an array of theatrical costumes, from Santa garb to nurse outfits.

Beneath her boisterous facade, glimpses of vulnerability surface—confessing loneliness during a sleepover or revealing insecurities tied to her status as an only child with rarely mentioned parents. Her envy of Ana and Matsuri stems from craving validation, particularly from Nobue, whom she idolizes despite their clashes.

Quirks include a childhood history of demanding implausible gifts from Santa (a mountain, a sumo wrestler), later boasting she "defeated" him. Born September 8th, she sporadically showcases odd logic, like advocating post-bath stretches, though such moments drown in her trademark absurdity—toilet humor, communal bath fart jokes, and irreverent antics.

While her relationships teeter on chaos, the group tacitly tolerates her provocations, cementing her role as an abrasive yet fixture presence. Even her most disruptive acts betray flickers of sincerity, hinting at a buried longing for connection beneath the clamor.