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.

Karas: The Revelation is about the battle between supernatural forces on the streets of modern-day Japan. The Revelation covers the true identity of newly-minted Karas (spiritual protector of humanity from demonic forces) Otaha, who returns to his hometown to rescue a friend from gangsters. Meanwhile, evil Karas Eko continues his campaign of terror against mankind with the aid of a multi-headed dragon summoned by the powers of rogue demon Nue.

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.