Taken into the care of the Makimura family after the death of his parents, Akira Fudo is leading the life of a high-school student when, upon the death of the father of his good friend, Ryo Asuka, he undergoes fusion with a demon, but through strength of will retains his human spirit to become 'Devilman'. Having the power of a demon, Akira shoulders his destiny of 'battle' to protect Miki, the girl he loves, and to save humanity. Taking possession of human all over the world and engaging in wholesale slaughter, the demons increase in power and influence. However, the people Akira should be protecting form so-called 'demon squads' who begin killing fellow humans. And then Akira sees none other than the one he should be fighting alongside, his friend Ryo, now becomes the demon 'Satan'.