Kotoha Aoyama is an elementary school student and one of the three founding members of a self-styled neighborhood peacekeeping group in the Ueno district. She serves as the recognized deduction specialist of the trio, the member most drawn to logical challenges and the one who puts the greatest effort into solving the puzzles and mysteries that arrive at the group’s makeshift headquarters. Her outward demeanor is often cool and composed, giving her a reputation as the brains of the operation, and she genuinely enjoys books, brainteasers, and any activity requiring careful thought. At the same time, that composure is undercut by a distinctly childlike transparency: when frustrated, surprised, or amused, her reactions are swift and unhidden, swinging easily into tearfulness or helpless laughter. This blend of attempted seriousness and emotional honesty forms the core of her personality. She is also a devoted video game player who can be found with a handheld console whenever there is a lull in the group’s pretend missions, although it eventually becomes clear that her enthusiasm far outpaces her actual skill, and having that fact pointed out by her friends sends her into a prolonged gloom.

Her motivations stem from a genuine investment in the group’s shared fantasy of protecting the town, but more than that, Kotoha is driven by the simple desire to spend time with the two people she considers her most important companions. She approaches the role-playing scenarios with an analytical intensity that the others often lack, attempting to turn every errand and make-believe crisis into something solvable, yet she never places the mission above the friendship itself. In the group dynamic she often acts as a foil to her more impulsive or timid friends, providing the calm reasoning that keeps their plans from completely derailing, even as her own gaps in worldly knowledge remind everyone that she is still a very young child. Her closest relationships are with the other two Colors members: Yui Akamatsu, whose gentle and easily flustered nature Kotoha quietly accommodates, and Saki Kise, whose boundless energy she both reins in and quietly admires. She also shares an easy rapport with the local shopkeeper known as Pops, who supplies the group with riddles, contraptions, and trinkets, and she participates in the group’s often-antagonistic but fundamentally affectionate interactions with the neighborhood patrolman.

Over the course of the series, Kotoha’s hidden vulnerability receives more attention, particularly the contrast between her image as the clever one and her actual mediocrity at the very hobby that defines much of her free time. This revelation does not alter her role but does deepen the sense that her logical exterior is only one part of a much softer and more impressionable personality. Her notable abilities center on observation and deduction within the playful context of the group’s mysteries: she is the one who deciphers codes, interprets obscure clues, and arrives at the conclusions that resolve the group’s self-appointed cases. While these skills are modest in scale, they give her a distinct place within the trio and repeatedly nudge their games toward satisfying little victories. Consistent with the color-coding of the group, her everyday appearance features a pale blue dress, black leggings, white shoes, and a white hat with dark blue ear-like accents, and her long blue hair is one of her most immediately recognizable traits.