Kyōko Toshinō serves as a central figure in the narrative, introduced as a second-year middle school student at Nanamori Middle School. She sports long blonde hair consistently tied with a dark-red ribbon and has blue eyes. Her distinctive fashion sense embraces flashy costumes and cosplay outside school, such as a tomato-themed kigurumi pajama, while selecting animal-themed ones for friends.

Her personality radiates relentless optimism and high energy, driving her to act freely without regard for personal boundaries, though devoid of malice. She displays laziness toward academics but achieves high test scores through last-minute cramming. As a talented dōjinshi artist, she publishes under the pen name "Ramuko Nishikyogoku," focusing on her favorite magical girl anime character Mirakurun, and participates in events like Comiket. Her passions prioritize rum raisin ice cream and otaku culture over school duties.

Kyōko's childhood contrasts her current vibrancy; she was once timid, quiet, and easily distressed. Her transformation into an outgoing persona occurred at an unspecified time, supported by friends Akari Akaza and Yui Funami. Notably, Yui cut her hair short in their youth to appear tougher and shield Kyōko from bullies. This longstanding bond led Kyōko and Yui to co-found the Amusement Club in their first year, later joined by Akari and Chinatsu Yoshikawa.

Relationships deeply influence Kyōko's development. She harbors a persistent infatuation with Chinatsu due to Chinatsu's resemblance to Mirakurun, expressing this through hugs and playful teasing, often met with tsundere-like resistance. Despite Chinatsu's crush on Yui, Kyōko's enthusiasm remains unwavering. Her dynamic with Yui involves frequent physical comedy—Yui often hits her for antics—yet reflects mutual care; Kyōko intuitively senses Yui's loneliness when living alone and stays to keep her company. Ayano Sugiura, the student council vice president, secretly holds romantic feelings for Kyōko and views her as an academic rival, though Kyōko remains oblivious. She shares a lively rapport with Sakurako Ōmuro due to similar personalities, collaborating on activities like arcade visits.

Kyōko appears across all primary franchise installments, including every episode of the three main anime seasons, OVAs like *Nachuyachumi!* and *Nachuyachumi!+*, and the net animation *MiniYuri*. She also features in spin-offs such as *Tensei Shitara Akari dake Slime datta ken* and *Reset!*, albeit in supporting roles. Her narrative presence occasionally overshadows nominal protagonist Akari, particularly in early seasons where Akari's "lack of presence" becomes a recurring joke. Key episodes explore her reversion to childhood shyness after a head injury and recovery, her leadership in Amusement Club activities, and her efforts to bridge social gaps among peers.