Kaori Suzumiya, younger sister to Haruka Suzumiya, anchors her identity in fiercely protective family bonds. When Haruka endures a severe accident and slips into a three-year coma, Kaori demonstrates unwavering devotion through constant hospital visits. Her character transforms dramatically after Haruka’s awakening. Discovering that Takayuki Narumi and Mitsuki Hayase kindled a romance during Haruka’s incapacitation, Kaori reacts with visceral betrayal and rage, confronting both with scathing disapproval.

As a competitive swimmer, Kaori once idolized Mitsuki’s athletic prowess. This admiration shatters upon learning of Mitsuki’s relationship with Takayuki, igniting an internal conflict between past reverence and unwavering sisterly loyalty. Potential romantic feelings for Takayuki further complicate her emotional landscape, with narrative threads in the source material hinting at possible romantic outcomes, though inconsistently explored.

In the "Next Season" timeline, Kaori persists in swimming, frequently marked by her signature headband as both athlete and high school student. Her role shifts toward supporting Haruka and Takayuki through the aftermath of Haruka’s lost years and recovery. While her earlier confrontational edge mellows into familial support, traces of her protective instincts endure.