Koharu Sato is a high school girl who serves as the female protagonist of the story. She is a classmate of Sota Oshio, the male lead. Koharu is widely known throughout her school by the nickname Salty Koharu, a reputation she has earned because of her consistently cold, dismissive, and blunt demeanor toward everyone around her, regardless of their age, gender, or appearance. Her responses to social advances are famously curt, often consisting of short, unfriendly phrases delivered with a completely blank expression, which has effectively kept all of her classmates at a distance.

In terms of appearance, Koharu is considered exceptionally beautiful, striking a balance between cute and elegant that attracts a great deal of attention. She has black hair cut in a bob that falls to her shoulders with ends that gently curl inward, large almond-shaped eyes, and a well-defined nose. Her overall look is consistently well-groomed and put-together.

Beneath her forbidding exterior, however, Koharu has a very different personality that only a few get to see. She is surprisingly gullible and becomes flustered easily. She also has a clumsy side, being notably terrible at taking pictures despite her obvious efforts to do so, often wearing a smug expression as she attempts to get the perfect shot of her food. When she lets her guard down, she reveals a sweet and adorable side, such as when she genuinely smiles. Her cold demeanor is suggested to be a mask that hides a much more vulnerable and shy individual.

Her motivations are not explicitly stated, but her behavior implies a deep-seated discomfort with social interaction that leads her to push people away preemptively. Despite her prickly personality, she does have a desire to connect with others, as seen when she becomes upset and seeks comfort. Her role in the story is that of the primary love interest. The central plot is driven by the fact that she shares a mutual, secret attraction with Sota Oshio, though both believe their feelings to be unrequited. The narrative focuses on the slow deepening of their relationship as Sota discovers her true, softer nature, which she hides from the rest of the world.

Her most significant relationship is with Sota Oshio. Their dynamic begins to change after he helps her during a difficult moment when she is being harassed by male college students at the café where he works. In the immediate aftermath of this frightening incident, the tough, salty persona crumbles completely, and she breaks down in tears, hugging him for comfort. This event marks a turning point, as she begins to show him her genuine, less guarded self. Another key relationship in her life is with her cousin, Rinka Sudo, a third-year junior high school student.

Throughout the story, Koharu undergoes significant development. The narrative is built around her gradual transformation from a universally feared and unapproachable figure to someone who is capable of showing vulnerability, honesty, and sweetness, specifically to Sota. As their relationship progresses through shared school days and moments at the café, she slowly reveals more of her sincere and clumsy personality, moving away from the purely salty identity she had constructed for herself. Koharu does not possess any supernatural or notable combat abilities, as the story is a realistic slice-of-life romantic comedy. Her most defining traits are her social persona and her hidden emotional fragility. There is no information regarding her development beyond the general premise or any notable abilities she may have.