Kotonoha Katsura, Kokoro Katsura's older sister, originates from a wealthy family, a background that restricted her early social experiences. She exhibits distinctive physical traits: pale skin, maroon irises, and very long, straight black hair extending past her waist, coupled with a mature and notably voluptuous figure.

Her personality outwardly presents as intelligent, gentle, polite, and reserved, yet masks considerable emotional volatility. Extreme devotion to romantic interests, particularly Makoto Itou, defines much of her behavior; perceived abandonment or betrayal frequently triggers drastic psychological shifts into unstable or violent states, sometimes termed "yandere" manifestations. These can range from severe depression and suicidal ideation to homicidal actions targeting rivals.

Her interests and skills encompass extensive reading, often in libraries or bookstores, practicing iaido martial arts (implicitly enabling precise violence), and enjoying horror/splatter films despite her otherwise prudish demeanor. She struggles with general housekeeping but excels at making specialized lemonade learned from her mother. An intense aversion to physical contact with males appears early, though this diminishes if she perceives sexual activity as necessary to maintain relationships.

Within the original visual novel, her development varies significantly based on player choices. Paths exist where she remains relatively stable and devoted, becomes sexually assertive or manipulative, engages in blackmail, assists in covering up crimes, or descends into murderous insanity—often linked to whether Makoto remains faithful after initiating intimacy. Multiple endings depict her suicide, killing Sekai and/or Makoto, or maintaining polyamorous arrangements.

The anime adaptation intensifies her negative traits, depicting her being ignored and bullied after Makoto pursues Sekai. Following an implied rape by Taisuke Sawanaga during a school festival, she deteriorates psychologically, fabricating phone conversations with Makoto before he temporarily reconciles. In the climax, after Makoto callously rejects the pregnant Sekai by kissing Kotonoha in front of her, Kotonoha later murders Sekai by sawing her neck and abdomen open after Sekai kills Makoto.

The manga adaptation follows a trajectory similar to the anime, though Makoto attempts to atone after cheating. Kotonoha, already unstable, tries to kill Sekai but accidentally injures Makoto during the attack.

Within *Magical Heart Kokoro-chan*, she appears in a non-canonical parody context as "Magical Word," a superheroine aiding her sister Kokoro ("Magical Heart") against the villain Doctor S. She wears a very short kilt and tight-fitting suit, wielding a katana in battles against perversion-inducing zombie viruses and mecha. This role includes subtle awareness of Kokoro's secret identity and contrasts sharply with her usual persona through exaggerated action tropes.

Other media like *Summer/Shiny Days* and *Cross Days* explore alternate routes where she is romancable individually or in harem scenarios, sometimes showing bisexual interest in Sekai. *Cross Days* additionally depicts Yuuki Ashikaga developing a crush on her while she remains committed to Makoto.