Mayoi is a fifth-grade elementary school girl. She is 144cm tall and always carries a big backpack, wears a hairband, and sports ponytails. Befitting her age, Mayoi is cheerful, energetic and inquisitive. She makes a lot of spelling mistakes and has a habit of mispronouncing Koyomi's family name. On the other hand, she does not easily trust strangers, and will even fight back against them if they become too nosy.