demons are being un frozen by changes in climate and are killing peaple,Akira Fudo is a school kid whose mysteriose freind Ryo pops up and tells him "the only way to defeat a demon is to become a demon"
Akira joins with the warrior demon Amon but Ryo isnt able to (hhhmmm i wonder why?) Akira becomes the demon hybrid Devilman and destroys demons,saves the day all round good stuff.
Ryo starts to question Devilmans killing of demons saying that demons killing peaple is only natural because as a speacies we have no preditors to hunt us so spread like a plauge.
it latter turns out that Rou is really Satan in human form so he can learn about humanity and awaken when he decides it is time to bring an end to us as we have all doomed ourselves anyway.
(i get a little confused here cause even though anoughter demon awakens Satan early Satan hangs around and helps Devilman kill his demons instead of making the earth a demon paridise like hes supposed to (i guess hes got that awww ill do it tomorrow attitude) Ryo falls in love with Akira or devilman or Amon im not sure and this big demon guy with a bomb starts off world war III but no ones really that worried about it???)
for some reason Amon and Devilman become seperate entities and Amon tries to kill Satan/Ryo for trapping him in a human body
but Devlman stops him and tey both battle it out wish i could get a picture of that it was amazing