Kotone Himekawa is a reserved 15-year-old student with lilac or light purple waist-length hair (depicted as blue in "Remember my Memories") and scarlet or purple eyes, standing 156 cm tall with measurements of 77-54-78 cm. Her name translates to "Japanese harp sound." She possesses uncontrollable psychic abilities that manifest differently: in the original "To Heart" game and anime, she experiences precognition, foreseeing disasters affecting those close to her, while in "To Heart: Remember my Memories," her ability shifts to telekinesis, moving objects with her mind.

These powers cause significant social isolation. Ostracized by classmates who label her an "unheilsbringer" (harbinger of misfortune) due to poltergeist phenomena and strange occurrences since middle school, rumors lead to abandonment by most friends, leaving her primarily accompanied by a stray kitten. Her personality is gloomy, pessimistic, and dandere (quiet and introverted), expressing herself using "watashi."

Her romantic interests also vary: in the original series, she secretly observes the school soccer team from a distance due to a crush on its star player, Masashi. In "Remember my Memories," she confesses romantic feelings for the protagonist Hiroyuki Fujita, with no mention of Masashi. She enjoys eating udon noodles. Visually, she wears a sailor school uniform featuring an off-the-shoulder shirt, pleated skirt, ribbon tie, ankle socks, and loafers.