**Mayumi Furui** is a petite high school transfer student distinguished by her short light black hair, violet eyes featuring one protruding eyelash at each corner of her eyelids, and small thick eyebrows. Her uniform differs from classmates, consisting of a lilac sweater with an ivory neckerchief, a short black skirt, and short white socks.

Naturally high-strung and prone to worry, Mayumi occasionally joins the playful antics initiated by her friend Momoko. She exhibits a caring nature within their trio, often alerting others to potential problems.

Mayumi transferred to the school approximately one year before the main events. Initially seated beside Momoko, Mayumi found her intimidating and hesitated to approach. Their friendship began when Mayumi observed Momoko making shadow puppets by a river after school; joining in sparked an immediate bond. Momoko later introduced Mayumi to Shibumi, forming their close-knit trio.

In daily life, Mayumi participates in various activities with her friends: crafting animals from napkins in family restaurants, experimenting with poses on an abandoned skateboard, drawing on fogged winter windows, seeking shelter from rain, gathering for warmth and tangerines under the kotatsu at Momoko's home, and walking together after school. Her supportive nature surfaces in interactions like comforting Momoko during unlucky incidents and sharing food when Momoko lacks funds.