Mazinkaiser originally appeared in Super Robot Wars F Final, when developer Banpresto asked Mazinger creator Go Nagai to design a new mecha for Kouji to use as a Mid-Season Upgrade. The idea was for Mazinger Z to be upgraded through exposure to Getter Rays into a new monstrous form, later redubbing it the Mazinkaiser. Super Robot Wars Alpha, the next "major" installment of the franchise, revamped the origin of the robot into being the original Mazinger Super Prototype that ended up being too difficult to control, necessitating its sealing away until Kouji finds and tames it (this version also conveniently fills out the long-standing plot gap of "what was the accident that nearly killed Kenzo and his wife?" in Mazinger mythology). The idea was such a hit with fans that Nagai quickly incorporated it into canon in anime and manga form, using the Alpha version as its origin story.
During a massive attack by Mechanical Beasts created by Mad Scientist Dr. Hell, the Mazinger Z and Great Mazinger sortie to battle, but are overrun through sheer numbers. Kouji's Hover Pilder is ripped from the Mazinger Z and hurled from the battlefield, and the machine is captured by Dr. Hell, who turns it into a mechanical devil for his own purposes and sends it against the Photonic Research Institute. Outnumbered, Tetsuya Tsurugi heads to battle with a damaged Great Mazinger when a new, insanely powerful and more demonic looking Mazinger suddenly appears with Kouji at the helm.
The seven-episode OVA was followed up by the movie Mazinkaiser vs. The Great General of Darkness, a remake of the 1974 film Mazinger Z vs. The Great General of Darkness, where the Mycenae Empire invades while Kouji is vacationing in Paris, forcing him to fight his way back to Japan and take the Mazinkaiser into battle once more. Said movie canonicity to the OVA is ambiguous, with it not even using the same version of the Mazinkaiser mecha, though Super Robot Wars installments since Super Robot Wars Judgment have used them together.
See also Mazinkaiser SKL, a three-episode OVA released in 2011, an entirely different re-imagining with all-new characters.
- Adaptational Wimp: In the original Mazinger manga, Venus was a huge step up from Aphrodite A, allowing Sayaka to destroy several mechanical beasts and helping Kouji fight Gordon Hell. In Mazinkaiser it being more powerful is nothing more than an Informed Attribute, being defeated just as often as her old mecha.
- Adapted Out: Count Blocken, Hell's usual second-in-command alongside Ashura, doesn't seem to exist at all.
- All Your Colors Combined: In the first episode, Mazinger-Z and Great Mazinger used their Chest Blaster weapons in combination to melt a Mechanical Beast to slag.
- And This Is for...: Kouji finishes off Ankoku Daishogun with this.
- Ascended Extra : The blonde twins Lori and Loru. Back in the original manga, they were nothing but Red Shirts who last for 2 chapters. They fill the same role in the movie, but in a more glorious manner.
- Beach Episode: Infamous for its brief, nude moment with Sayaka in episode 4.
- Big Bad: Baron Ashura serves as this, while Dr. Hell serves as a Greater-Scope Villain of sorts.
- Big Damn Heroes: The true Great Mazinger in the last few episodes.
- Tetsuya does this in the first episode too.
- Boss, in the last episode and the movie.
- The Blade Always Lands Pointy End In: Made in an EPIC way in Mazinkaiser vs. The Great General of Darkness.
- Bloodier and Gorier: Mazinkaiser vs. The Great General of Darkness in spades. From the Family Unfriendly Deaths of Lori and Loru to numerous Red Shirts being sliced in half.
- Boomerang Comeback: Great Mazinger pulls one off in the movie.
- Breath Weapon: Rust Tornado, a version of Mazinger's Rust Hurricane, combined with Great Mazinger's Great Typhoon: Mazinkaiser blows several jets of particle-charged wind from its mouth grill that corrodes the enemy into nothingness (assuming the terrifying gale winds did not break it apart first). Its huge destructive force dug a ditch through a side of Mount Fuji.
- Brought Down to Badass : For some reason, Tetsuya switched back into old Great Mazinger in the movie. He's still as kickass as ever.
- Canon Immigrant: Everything that could be explained about this one has already been addressed on the page description.
- Convection, Schmonvection: In the last 2 episodes, Mazinkaiser gets dunked in lava. Since Mazinkaiser is Made of Indestructium, Kouji can survive for a short while in that enviroment, but everyone knows they had to get him out of the volcano quickly, or he would die. Averted with Mazinkaizer's Fire Blaster, which melts foes even when the visible beam misses them entirely.
- Death by Adaptation: If the OVA episodes do not share the same continuity with The Movie, then Dr. Morimori, Lori and Loru are taken out in the latter while more or less surviving in the former.
- Distracted by the Sexy: It happened fairly often in the original manga. Usually it was Sayaka who was the (unwilling) distraction -either because her clothes were torn or because she was involuntarily naked-, but sometimes it was done by enemies to distract Koji. One of those scenes was animated in the Beach Episode: Kouji accidentally undoes Sayaka's topnote ; she's actually more upset by Boss getting a look at her breasts than she is by Kouji, even though he weaponizes her boobs in order to escape the enemy fortress.
- Dragon-in-Chief: Although they are Dr. Hell's Dragon, Baron Ashura more or less behaves as the story's main antagonist.
- Exactly What I Aimed At: In the movie, Tetsuya is fighting Angoras and Scarabeth, two commanders of the Mycenae Empire army. Tetsuya throws Great Mazinger's Great Boomerang and right after shoots Great Typhoon. Both attacks miss, both commanders laugh and ask where he is aiming at... when Great Mazinger's boomerang slices them both from behind. As he is dying, Scarabeth -Mycenae army's best tactician- realizes Tetsuya had missed his boomerang throw on purpose, and he shot Great Typhoon to change the boomerang's trajectory. So he caught them by surprise and killed both of them at once.
- Family-Unfriendly Death: Lori and Roll in The Movie, which doubles as Tear Jerker.
- Fan Disservice:
- Baron Ashura naked scene. Fortunately for us, it doesn't show the squicky bits at all. In fact, it's hilarious in context.
- The Beach Episode has Boss in a swimsuit.
- Fanservice: Sayaka and Lori and Roll in the Beach Episode, especially with the topless scene of Sayaka. Let's face it, that was probably the main reason this episode was made. Especially when you consider that when it happens, they play it up like someone just found the Ark of the Covenant.
- The Guards Must Be Crazy: Apparently Baron Ashura's mooks can't tell the difference between Boss in a helmet and one of their co-workers. The mooks that were assigned to guard him and Kouji specifically, no less.
- Hoist by His Own Petard: In episode 5, Baron Ashura detonates multiple bombs they set at the Photon Research Institute...only for Boss to reveal that he gathered them up into a briefcase and hurl them at Ashura just before they go off.
- Hotter and Sexier: This show has more fanservice than any adaptation of Mazinger Z, especially the episode 4 that has sexual humour and nudity.
- Large Ham: If the dub acting was any hammier, you could serve it for Christmas dinner. Special attention goes to Dr. Hell, who is chewing so much scenery that his fortress should be collapsing around him.
- Latex Space Suit: The pilot suits for both the male and female characters.
- Lava Is Boiling Kool-Aid: In one episode Mazinkaiser (with Kouji inside it) was tossed into the crater of Mount Fuji (paying homage to an episode of the original series). Kouji fainted due to the extreme heat and sheer pressure... and that was it. The characters pointed out not even Mazinkaiser could endure that for long and they had to get Kouji out of the magma RIGHT AWAY, though. However, given the kind of punishment Mazinkaiser shrugs off throughout the series, withstanding a lava bath seems almost trivial.
- Let's Get Dangerous!: The twins Lorru and Lori when it's time to get serious.
- They also show their stuff in the movie, what with piloting a Robot and all. Too bad that's where they die.
- Made of Indestructium: Mazinkaiser takes this concept and runs with it. Nothing seems being capable to even scratch it. This video should show it convincingly: 
- Go Nagai himself has remarked that Mazinkaiser is the "indestructible shield" while Shin Getter is the "unstoppable sword", a reference to the Chinese version of the irresistible force paradox.
- Mad Scientist: Dr. Hell. Juzo Kabuto was one, as well.
- Male Frontal Nudity: At the beach, there's a very jarring Extreme Closeup of Boss's scrotum poking out of his undersized swim briefs.
- Mooks: Iron Masks.
- Ms. Fanservice: Two of them: Loru and Lori. Sayaka also had her moments, specially the fourth OVA episode.
- Mythology Gag: The second ending theme shows a cross section of the Mazinkaiser, on what appears to be a Lego background, exactly like the ending of the original Mazinger Z anime.
- Put on a Bus: Tetsuya is written out 2 episodes in to recover from injuries and repair the Great Mazinger. He returns in grand fashion in the final episode.
- Redshirt Army: The Mazinger Army in the movie
- Robeast: The Mechanical Beasts.
- Shoo Out the Clowns: Inverted. The first two thirds of the movie are very dark. Then Boss comes back. The rest is history.
- Showy Invincible Hero: Taken to the limits with this. Mazinkaiser, the ultimate defensive force according to Go Nagai, is still awesome to watch in action thanks to great music and creative opponents.
- Spoiler Title: Played for Laughs; episode 4's "next on" section announces that the next episode will be named "Kouji Kabuto Dies in Magma", to the shock of Kouji himself. He doesn't actually die.
- Super Mode: The SRW version has two: "Devil" mode, which makes the Mazinkaiser go sentient and berserk, and "God" mode, which is theorized to be on par with a full-powered SRW Shin Getter Robo). SRW games also has Mazinpower that activates at 130 will giving a power boost.
- Taking You with Me: In Mazinkaiser vs. The Great General of Darkness, Roll uses her final moments to activate the Million Alpha's self-destruct function and kills General Birdler in the process.
- Telescoping Robot: Mazinkaiser had theee blades hid into its body (two of them into its shoulders and the bigger into its chest), and its midsection stored one giant missile.
- Truer to the Text: Despite the introduction of Mazinkaiser, in some ways this is closer to the original Mazinger Z manga than the TV series - like a much closer art style to Nagai's, and Gamia Q appearing.
- Tsundere: Variation. Sayaka was a Type A (tsuntsun) in the original series, but she mellows out a bit and is mostly a Type B (deredere), like in the manga.
- Use Your Head: Tetsuya used it with Kouji in the manga. Agreed, both of them were riding their respective Humongous Mecha, but still...
- Villain: Exit, Stage Left: Subverted; Dr. Hell prepares to escape his exploding lair in the final episode, only for his escape pod to be caught in the explosion.
- Walking Armory: Mazinkaiser's arsenal consists of...
- BFS: The (Final) Kaiser Blade from the OVA.
- Breath Weapon: The Rust Tornado, which still has the corrosive component
- Chest Blaster: The Fire Blaster; notably, it's theorized the Fire Blaster can punch a hole through to the Earth's core; it's so powerful that even though the main blast goes over a bunch of mechanical beasts, the sheer heat of it still melts them anyhow).
- Also technically the Gigant Missile, though it comes from Kaiser's navel.
- Dual Wielding: The paired Kaiser Blades from the movie; the Super Robot Wars original version calls them Shoulder Slicers.
- Eye Beams: The Photon Power Beam, which doesn't get a new name.
- Kill It with Ice: The Freezing Beam from the movie.
- Power Fist: The Kaiser Knuckle in the movie.
- Precision-Guided Boomerang: In the movie, the Kaiser Scrander can be pulled off and used as one. It even slices cleanly through the flying fortress Demonika.
- Rocket Punch: The Turbo Smasher Punch which, like Great's Screw Crusher Punch, makes everything better by spinning.
- Sphere of Destruction: The Kaiser Nova from the manga (and Super Robot Wars), where Kaiser charges its Photonic Energy to full power and releases it in a single gigantic burst.
- The Worf Effect: Both Mazinger-Z and Great Mazinger suffered this within the first two episodes, with both machines falling to Dr. Hell's Mechanical Beasts' army. Also, Tetsuya had been established in both Mazinger Z and Great Mazinger like a highly-skilled Ace Pilot, Combat Pragmatist Blood Knight and The Determinator, Hot-Blooded badass. In Mazinkaiser the animators showed a situation was dangerous and an enemy a real threat by severely injuring or incapaciting Tetsuya, or showing him struggling.
- The Movie took it even further by crushing Great, Venus, and the Mazinger Army. At least half of them didn't survive.