Yōko Inokuma is a central figure in the series, part of Shinobu Ōmiya's childhood friend group since elementary school. She cares for twin siblings Kōta and Mitsuki Inokuma, habitual liars whose antics sometimes worry her despite her protective nature. Her surname Inokuma combines the characters for "boar" and "bear," while her given name Yōko means "child of the sun," reflecting her sunny disposition.

Athletic and taller than most peers, Yōko favors practical, casual clothing like shorts or pants. Her school uniform includes a light blue buttoned vest and white tube socks. A distinctive feature is her visible canine teeth, especially noticeable when she lies. Energetic and fiery, she serves as the group's frequent tsukkomi (straight man) in comedic moments. Academically average, she requires tutoring, notably from Aya Komichi during exams to avoid repeating past failures.

Generally level-headed and adaptable, Yōko balances her friends' antics with responsibility, valuing cooperation and maintaining high spirits. She displays denseness regarding Aya's romantic feelings, unintentionally teasing her and provoking blushes. Despite this obliviousness, she deeply cares for Aya, worrying when she seems down and gradually becoming more aware of her feelings over time. She openly admires female aesthetics, remarking on enjoying women's curves and finding Alice Cartelet exceptionally cute, often complimenting her.

Key relationships drive her development. Her bond with Aya strengthens after Shinobu's temporary move to England during middle school. Though attentive to Aya in childhood, Yōko later shows denseness; a pivotal moment occurs when she dismisses a love letter's importance by declaring, "I'd much prefer just being with you, Aya!!" She eventually attends the same college as Aya and Karen Kujō.

With Shinobu, Yōko acts as a surrogate older sister due to her responsible nature, though their interactions lessen as new relationships form. She finds Alice adorable yet remains honest in feedback. Her similar personality to Karen fosters lively camaraderie, amplifying her energetic traits. Isami Ōmiya designates Yōko as a temporary big sister for Shinobu when unavailable, reciprocating by becoming an older sister figure to Yōko.

Her development across media shows gradual maturation. The *Pretty Days* OVA explores her middle school dynamic with Aya and Shinobu. During the second season, she supports Shinobu emotionally during Alice's absence by organizing a sleepover. By the manga's conclusion, attending college with Aya and Karen showcases her priority on enduring friendships. While never overtly reciprocating Aya's feelings, her awareness of them grows, culminating in a nuanced understanding of their relationship.