Shiki is a young woman who is descended from the Ryougi clan of demon hunters. Members of the Ryougi clan are born with multiple personalites; in Shiki's case, she has a calm and stoic female persona named 'Shiki' (式), and a warm and outgoing male persona named 'SHIKI' (織), who knows nothing but an urge to kill. At a young age, Shiki was chosen to succeed as the head of the Ryougi family because her older brother could not manifest another personality.
However, while she is in high school, Shiki is hit by car, killing the SHIKI persona and putting her into a coma for two years. After awakening, she is afflicted by a sense of loneliness due to SHIKI's absence, though she retains his murderous feelings. The near-death experience also gives Shiki the incredible power of the Mystic Eyes of Death perception, which she fears at first, but is later taught by a magus named Touko Aozaki to control. Shiki's classmate and love interest, Mikiya Kokutou, who waited for Shiki the whole time she was comatose, urges her not to give in to her instincts and kill a human being.
After leaving the hospital, Shiki goes with Mikiya to work for Touko Aozaki at the Garan no Dou detective agency, which deals in abnormal and supernatural cases. She uses her abilities to defeat demons, evil spirits, and other hostile entities.
Mystic Eyes of Death Perception
Shiki awakens from her two-year coma with the Mystic Eyes of Death perception, an ability that allows the user to perceive the death of something, living or nonliving, in the form of lines and dots on the target that, when cut or stabbed, will cause the object to be sliced and killed with ease or, in the case of the dots, erase a being/object's entire existence completely.
Shiki shares her given name and Mystic Eyes power with Tsukihime protagonist Shiki Tohno. However, Ryougi's eyes are more powerful than Tohno's because she can activate or deactivate them at will, and using them does not cause her any distress or pain. In addition, whereas Tohno can only kill physical targets, Ryougi can "kill" concepts or things without a physical form, such as when she is able to kill a demon possessing her body by seemingly stabbing herself in the chest, but leaving no harm to her physical body, or when she "kills" a disease inside of a young girl.
TYPE-MOON writer Kinoko Nasu states that there can only be one user of the Mystic Eyes of Death Perception; Kara no Kyoukai and Tsukihime take place in alternate universes.
Appearances in games
Shiki appears as a playable character exclusively for the PS2 port of Melty Blood: Actress Again and both versions of Melty Blood: Actress Again: Current Code. Her stage is the bamboo forest outside of her childhood home and its background music is her theme from the Kara no Kyoukai movies.
Shiki appears as a secret boss in Fate/Extra. She claims to have killed ninety-nine participants of the Holy Grail War and seeks to kill one more in order to return to her world.