Shiki was born into a secret assassins cult, but was quickly transferred to a place where they raised exorcists as they seemed it would be a place more fit for someone like her. She was already quite skilled as an assassin and thus mainly continued her training learning the ways of the Duo there. She introduced Sam to the exorcist life, and trained alongside him to become exorcists.
While Shiki may come across as cruel to some persons, she really is a genuinely nice person, most of the time. She is an observant type who expresses her feelings occasionally, but often doesn't feel the need to express them, but does not hide them either. She likes good sarcastic remarks, and is no stranger in making them herself. She is straight-forward, which someone might experience as harsh. She has a photogenic memory, being able to recall everything that has happened in her past. She can quickly become negative towards things, but always gets a kick out of fighting.
Because of her training as an assassin, she already was quite skilled in stealth. While not being able to enhance her abilities like Iwao, she still is quite fast and can move unnoticed in shadows, despite her pink hair. Her main weapon is a giant needle which she uses alongside a string for performing quick combo attacks. In addition she has a photogenic memory.