The OVA is based on the first volume of a 40 (!) volume light novel series by Maeda Tomiko, it tells the story of Laethreel (or just plain Lath), a wannabe demon-breaker who controls a powerful sword, Gurenki, but not much else. She suddenly acquires a "protector", Anshu, and a mission: to rescue the kidnapped princess of Gandia from the clutches of the jet-black demon Aju. However, Laethreel shares a dark secret with her younger brother Leedyle, and her mission proves more complicated, and dangerous, than it first appears.—myanimelist