Kukuri Tachibana is a third-year student at Kouryoukan Academy and the adopted daughter of a well-known local novelist, from whom she received her surname. Her appearance is strikingly identical to Kakeru Satsuki’s late older sister, Kukuri Satsuki, which immediately creates confusion and emotional tension for him. She is one year older than both Kakeru and Yuka Minase. She lost her voice under unexplained circumstances and has no memories of her life before the age of thirteen, so she communicates exclusively through writing in a sketchbook she always carries. Her demeanor is gentle, easy-going, and quietly kind; her muteness adds to an air of innocence that makes others feel protective toward her.

As one of the individuals drawn into the mysterious and hostile alternate dimension called the Red Night, Kukuri possesses a unique supernatural ability: she can project her soul into the form of a chained angel she calls Abraxas. Abraxas wields sharp bladed chains to attack enemies and can also provide potent healing, making her a versatile protector in battle. Despite her soft outward nature, she willingly fights alongside the group to survive the Red Night’s dangers.

Her most significant relationship is with Kakeru Satsuki. Because she looks exactly like his deceased sister, he is initially convinced she must be Kukuri Satsuki returned, but Kukuri Tachibana herself denies this. Over time, the true nature of her existence becomes clear. In the anime adaptation, she is not an alternate-reality version of his sibling but an illusion brought into being to comfort Kakeru during his grief and inner turmoil. She acts as a quiet, steadying presence, giving him emotional support when he needs it most. As Kakeru gradually grows stronger and comes to terms with his loss, her purpose is fulfilled, and she fades away peacefully. Her departure marks a turning point in his personal development, symbolizing his ability to move forward without depending on a comforting fantasy.

Thus, Kukuri Tachibana is defined by her ethereal origin, her selfless dedication to Kakeru’s emotional recovery, and her graceful acceptance of her own transient nature. Her abilities with Abraxas and her silent, sketchbook-based communication reinforce her otherworldly, fragile quality, while her kind heart leaves a lasting impact on those who knew her during the Red Night.