Rin Kurenai is a 17-year-old human female with long red pigtails and red eyes. On duty, she wears a yellow-green military coat with knee-high boots; during civilian activities, she dons a school uniform of a skirt, white elbow-length shirt, and ribbon-tied collar. Her parents died in a fire during the Great Destruction ten years before the main story. Believing protagonist Eiji Hoshimiya responsible, she forged an intense grudge that drove her to become a Dazaifu Central Bureau assassin with the rank of Second Lieutenant. Her mission: infiltrate Eiji’s high school as a transfer student and eliminate him. Rin wields an Order ability called "Rebirth Fire" or "Flame of Resurrection," granting functional immortality through rapid regeneration. She recovers from fatal injuries like stomach impalement or forehead gunshots. The power also heals others, as shown when she inadvertently mended Eiji’s stepsister Sena Hoshimiya’s torso wound. Initially audacious, impulsive, and ruthless, Rin employs violence without hesitation—stabbing Eiji’s hand or taking Sena hostage via impalement. She disregards comrades’ safety while pursuing goals and declares exclusive rights to kill Eiji, displaying yandere traits. After repeated failed assassinations, Eiji subdues her using his "Bind Dominator" Order. This compels her to stay within his domain indefinitely, forbids harming him or Sena, and accidentally designates her as his life partner. Physically constrained, she defies emotional control and seeks loopholes for indirect kills. These attempts often backfire, causing her repeated deaths followed by regeneration. Forced proximity reshapes her dynamic with Eiji. While persistently vowing to kill him, she aids his prison escape and navigation of Dazaifu Central Bureau facilities. Learning Sena caused the Great Destruction shifts her vengeful focus, yet she continues collaborating with Eiji against common threats. Rin gradually develops ambiguous feelings toward him, blending hostility with cooperation and physical intimacy like crotch-grabbing or ear-biting from supplemental media. Their complex relationship intertwines reluctant partnership, romantic tension, and unresolved vengeance.