Kaori Himekawa is a skilled second-year swimmer at Umineko Shōgyō High School, nearly winning the Kantou Tournament's 200-meter event the year before the series begins. She possesses dark green hair and grey eyes. Though admired by male students, she reacts to being stared at with significant self-consciousness, visible discomfort, and embarrassment. This contrasts with a recurring trait of secret promiscuity, shown through habits like wearing revealing lingerie under her school uniform and collecting Japanese kokeshi dolls in her bedroom. She also exhibits a behavioral quirk of gazing at members of the opposite sex or objects resembling masculine forms, such as statues or large horns.

Her family environment, revealed during teammate Kaname Okiura's home visit, features parents openly engaging in sexual roleplay, suggesting a possible influence on her behavior. Her grandfather founded the prominent Shizu Group. During interactions with Kaname Okiura, she develops ambiguous feelings, though their nature or progression remains undefined. Throughout the series, she functions primarily within ensemble comedic scenarios centered on the swim team's activities. Her character lacks significant development, expanded backstory, additional narrative arcs, personal evolution, or background revelations across the manga, anime television series, or other official media beyond her established role as a supporting team member with these personality traits and familial context.