Divided into four installments.
I love this series! It's a great combination of sci-fi, fantasy, horror, cute girls, combat, sorcery, romance, drama, and humor. Hazumi Jinno is, of all things, just a normal female high school student who is in charge of protecting the "master key" from creatures from the dark world. She wields a big nasty "soul sword" and usually frightens her classmates as much as her enemies. Lots of hilarious characters and great moments, and Hazumi is very cute with keen fashion sense.