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.

Tatsumaki is the S-Class, Rank 2 superhero and the older sister of Fubuki. Tatsumaki is a petite woman, commonly mistaken for being much younger than she really is. She has a youthful face with wide emerald green eyes and hair that curls up on the ends. She wears a formfitting black dress with long sleeves and four high-cut leg slits that show off her legs and low-heeled black shoes. Being the second ranked S-Class hero, Tatsumaki is very powerful. She is one of the most powerful heroes and the most powerful esper alive. Fubuki describes her as a monster much like Amai Mask, who chooses not to advance from A-Class to S-Class to not allow weaklings to rank up. Even after witnessing Saitama's display of power in the fight against her, Fubuki is convinced that Saitama is nowhere near her older sister in terms of strength and fighting ability. (Source: One Punch-Man Wiki)