This explanation is my culmination based on my 3 viewings of "Karas: the Prophecy", and four website explanations: Netflix, IMDb.com, and a quoted DVD text, and the official (English) website. Please note that this explanation is based on the English texts I have read and the English translation of the movie. It may not be 100% accurate, which if I have done this correctly, a more accurate explanation would really require knowing Japanese. E.g. "Eko" is actually Eku, and Yurine, is really "Yuri" and from the little Japanese I know, a single letter can drastically change the entire meaning of a word. OK, enough said.
= THE PROPHECY = It was once foretold, that the battle for the future world will start and end - with Karas.
= THE PLOT = The worlds of humans and demons have overlapped since time immemorial, and a spirit named Yurine (who represents the will of the people in the city) and her servant, Karas, have long maintained order and balance between the worlds. But humans have finally lost their beliefs of the demons and spirits. Disgusted by human arrogance, Karas turns his back on his role as guardian of the city, taking the name Eko, and plans an attack against the humans in the city. His goal is to have the humans once again believe in, and fear, demons.
Eko and his followers live in the material realm in human form, but to continue doing so they must feed on the fluids of human bodies. Their periodic feasts result in massacres that leave only a single traumatized survivor. (There is no explanation given for this - it might be part of Eko's plan to re-instill fear into the hearts of humans.)
Opposing Eko is the once demon Nue, who also lives in the material world in human form but refuses to drink blood. He wants to kill Eko b/c Eko trapped Nue's younger brother to help complete his evil plan. Also opposing Eko is Otoha, a human, who called out from his heart to Yurine - while he lies in a hospital bed in a coma. They make a contract and he becomes the new Karas.
= THE KARAS = The "Karas", which means "crow" in Japanese, is their nom de plume as well as their title. There are others called Karas as well, Eko and Otoha are just the two most current and powerful. They can transform into any of various heavily armed vehicles. (There is much about "crows" but a lesson in ancient Japanese culture may explain that thread.)
= The Humans = These "inexplicable" tragedies are the obsession of a marginalized police inspector whose daughter was the survivor of one such massacre. A young Leutenant is assigned to this "department". Beyond this simple role, they hardly have anything to do with the plot.
Final comment: the first one is: "Karas: the Prohpecy" which has phenomenal CGI and action. 5/5* the second one is: "Karas: the Revelation" which has a cheaper version of the first CGI and typical anime action. 3/5*
-LD
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my faith: http://www.angelfire.com/ny5/jbc33/