Devilman (1987)

Normal life in modern day Tokyo is unexpectedly disrupted for a young high school kid called Akira. First his parents go missing, then his pet rabbit is viciously slaughtered and finally his best friend, Ryo Asuka, reveals a terrifying secret--something that guarantees that Akira's life can never be the same again. Ryo's dead archaeologist father left him a dark and sinister legacy, knowledge of which may only condemn Ryo in the same way it condemned his father--to an eternal sentence of suffering and torment. However, Ryo understands that his legacy also has the power to salvage the human race from torturous damnation at the hands of demons. But whoever kills a demon must become a demon and only one who is pure of heart can possess the body of a demon--only one like Akira!