Kotone Shirakawa, the younger of the Shirakawa sisters, stands at 153 cm with brown eyes and black hair trimmed to her neckline. Her striking figure, marked by a 90 cm bust and G or H cup size, leads to recurring challenges with clothing fit. Though she projects a relaxed demeanor, Kotone harbors a mischievous streak, earning her a "little devil" reputation through audacious or teasing actions that contrast her quiet exterior. This duality defines her interactions with Kazushi Sudou, a childhood friend she and her sister Ayane regard as an older brother figure. Kotone initiates playful teasing and physical closeness with Kazushi, though glimpses of vulnerability surface when her unspoken feelings emerge.

Her relationship with Ayane intertwines sibling rivalry with their shared devotion to Kazushi. While Ayane adopts a guarded approach, Kotone openly displays affection, both vying for his attention. Kotone’s emotional layers emerge in her quiet resolve to accept a secondary role in Kazushi’s life if it ensures her place beside him—a blend of reluctant compromise and unwavering resolve.

Narrative threads explore her navigation of increasingly intimate scenarios with Kazushi, from shared baths to private encounters, often laced with awkward humor. These moments blur the line between heartfelt connection and impish teasing, as she employs physical proximity to bridge emotional gaps.

As a high school student with years of shared history alongside Kazushi, their bond allows candid interactions. Details like her culinary preference for cream stew and her habit of addressing Kazushi as "Onii-chan" deepen her characterization, anchoring her in a blend of youthful spontaneity and quiet emotional depth.