This movie combines multiple different Go Nagai series, specifically Mazinger Z and Devilman. The plot is pretty straightforward; the Devilman demons are treated like kaiju, and the movie features a typical "bad guys teaming up" storyline. I found that I was able to enjoy the movie without any prior context, as there was not much character or relationship development, and not much happened in terms of character or story progression. The animation quality varies throughout the film, but the character designs are excellent for its time. It's always a pleasure to see Go Nagai's design work animated, even if it's toned down for a youngeraudience.