One of the first installations of the Nasuverse and the spiritual precursor of both Tsukihime and Fate/Stay Night. The story is centered on Ryougi Shiki, a girl who, after having a near-death experience, can lines of death, which signify the end of anything she perceives. With these Mystic Eyes of Death Perception she can kill virtually anything with just a simple knife, from ghosts, to physical objects, to abstract concepts. She works under Touko Aozaki and solves various Magic-related mysteries, typically involving violent murder.
Powers of the Verse
As for the power standing of the series, it can be called both the weakest and strongest Nasuverse setting. While KnK definitely has some characters with powerful hax, they tend to fair poorly when matched with the massively superior physical capabilities of the later introduced servants. However, Shiki's third personality, as an avatar of a multiversal entity with claims to be able alter the nature of the universe, may be one of the more powerful characters in the verse, although this is confounded by lack of ample feats as well as contradictory Word of God.