In the year 2075, mankind has reached a point where journeying between Earth, the moon and the space stations is part of daily life. However, the progression of technology in space has also resulted in the problem of the space debris, which can cause excessive and even catastrophic damage to spacecrafts and equipment.

In the city of Shinjuku, a conflict between a rouge Karas by the name of Eko and the "will of the city" rage in a conflict for dominance. A Karas brought about to fight the rouge has fallen, leaving the city and its inhabitants defenseless. Soon after, Otoha, a comatose patient, is chosen to become a new Karas to face off the rouge Karas Eko to decide the fate of the city and its inhabitants.

Louise Françoise Le Blanc de La Vallière’s name is so long and her spell-casting skills are so poor that everyone at the Tristain Academy of Magic just calls her “Louise the Zero.” Louise’s humiliation only increases during an important second-year test, she inexplicably summons Saito Hiraga, a totally normal teenager from Tokyo. Now she’s stuck with him and Saito’s stuck with the lousy life of being a familiar.

When mecha attack a research center, its students, pilots, and researchers must fight back with the help of mysterious artifacts and a young samurai.

Tokyo: a city populated by both humans and ghostly beings. They exist in both dimensions, seen and unseen: spirits, apparitions, demons. The balance between these two dimensions has long been upheld by the city's guardian crow Karas and his masters. But that balance has been thrown into disarray as Eko, a former Karas, has attempted to seize power and bring order to the streets through force. The entity Yurine, who represents the will of the people, stands in his way with her newly risen Karas. Now an ageless battle stretching across both dimensions and killing humans and spirits alike is in progress. Karas is humanity's last hope.