Yōko Inokuma, a central figure throughout the *Kin-iro Mosaic* television series, OVAs, and film *Thank You!!*, possesses auburn hair, chestnut-brown eyes, stands 163 cm tall, and features a distinctive fanged tooth. Her school uniform includes a light blue buttoned vest and white tube socks, while casual wear favors less feminine shorts or pants. Born August 20 with blood type O, she has twin younger siblings, Kōta and Mitsuki Inokuma, whom she deeply cares for despite their lying. Having grown up with Shinobu Ōmiya since elementary school, she views Shinobu protectively due to her friend's occasional absentmindedness. Shinobu's older sister, Isami Ōmiya, acts as a surrogate older sister to Yōko.

Energetic, athletic, and consistently high-spirited, Yōko values cooperation and exhibits a boyish, carefree demeanor balanced by level-headedness, making her one of the group's more grounded members. She proactively befriended the shy Aya Komichi in middle school, helping her open up and establishing Yōko's pattern of social support. While generally observant, she remains oblivious to Aya's romantic feelings for much of the series, frequently teasing her unintentionally and causing blushes, though she worries when Aya seems down and consistently demonstrates deep care for her well-being. Academically, she struggles with grades and displays clumsiness, sometimes damaging belongings. She is also a big eater, occasionally consuming her lunch before school.

Her relationships extend widely. She openly adores Alice Cartelet for her cuteness while remaining honest with her. With Karen Kujō, she shares a lively dynamic, matching her energy and interests like food, developing a strong camaraderie. She interacts supportively with Honoka Matsubara and teachers like Akari Kuzehashi, reflecting her adaptable social nature.

Subtle developments occur across the series. Yōko gradually becomes more aware of Aya's feelings, though full reciprocity remains ambiguous. She aids Shinobu during emotional lows, such as organizing a sleepover to alleviate Shinobu's loneliness when Alice visits England. Her growing maturity is evident in prioritizing responsibilities, like studying with Aya to avoid repeating academic shortcomings. By the manga's conclusion and the film *Thank You!!*, she enters college alongside Aya and Karen, signifying continuity in their friendships and her ongoing role as a stabilizing yet spirited presence.

Her flower motif is the hydrangea, and a distinctive trait is showing her canine teeth when lying.