It's a crossover film between two of Go Nagai's most famous creations. (Cutie Honey's up there too, but this film was released three months before her anime debut.)
DEVILMAN = no, really. We're not kidding. He's not actually the Bible's Satan, but his best friend is. In 1973, he was also the hero of his own children's adventure anime.
MAZINGER Z = the first and groundbreaking (but not to my taste) super robot show, with a human pilot inside a mecha robot. There are also female pilots, but they fly mecha robots that have been styled to look feminine, with breasts. (Those are really chest-mounted bazookas, called Boob Missiles.) Why the gender stereotyping? Kouji and Sayaka Yumi should swap robots. Anyway, this film suggests that the best thing about Mazinger is its villains, with the luridly named Dr Hell and his habit of making weird lieutenants for himself.
Baron Ashura is half-man and half-woman. The dividing line is vertical, making one wonder nervously about what's inside his/her pants. S/he even has two voice actors, with either one (or both) delivering any given line depending on whether we're looking at the male or female face.
Imagine a much, much weirder version of Batman's Two Face. Dr Hell's other creations include Count Brocken (whose head isn't on his shoulders) and Viscount Pygman (who has a second, pygmy-sized torso instead of a head). They aren't in this film, though. We only have Dr Hell, Baron Ashura and some of Devilman's foes (Sirene, Zannin, Bugo).
The film made me smile by playing the oh-so-1970s manly Devilman theme song. Otherwise, though, there's not a lot here. Sayaka Yumi isn't exactly advancing the cause of feminism, but then again we've also got the giant, predatory Sirene sticking her hand through entire buildings. Akira and Kouji briefly live up to the movie's title when Akira trash-talks the Mazinger robot and Kouji takes the hump, which is resolved with a crazy motorbike stunt duel. (Akira points out that Mazinger can't fly, which was true at the time. The film then fixes that with the Jet Scrander, which as it happens the TV series hadn't introduced yet.)
The first half is okay. My attention drifted in the climactic big battle, but I woke up for the film's comedy punchline. "Devilman is still with us in our hearts!" I want to drive through America with that as a bumper sticker.
Overall, the film's fine. It's mostly pointless for anyone with a double-digit age, but it's doing what it says on the tin. It's so thick with 1970s anime earnestness that it's likeable even when being a one-dimensional macho cartoon. I'll be fond of anything with Devilman in it. It was successful enough to spawn other Mazinger crossover films, anyway.