Mazinkaiser: Shitou! Ankoku Dai Shougun
English title: Mazinkaiser VS Great General of Darkness
Japanese title: マジンカイザー　死闘！暗黒大将軍
Type: OVA
Episodes: 1
Source: Manga
Genres: Action
Studios: Brain's Base
Producers: Bee Media, Dynamic Planning
Duration: 56 min
Rating: R - 17+ (violence & profanity)

They strike without warning and instantly plunge the world into terror. The Great General of Darkness leads the underground Mycenae Empire in a bid to conquer Earth. The Mazinger Army falls before the seven generals under him, each of them leading an army of superior Warrior Beasts. Meanwhile, Archduke Gorgon is relentlessly pursuing Koji Kabuto, trying to eliminate him before he can reach Mazinkaiser. But a red light in the sky over Mt. Fuji portends the greatest battle in history!

(Source: Discotek)