It is played straight with Kenzo. His sons, Kouji and Shiro grew up believing their parents had died cause a laboratory experiment that went wrong. However, Kenzo's father saved his son's life by turning him into a cyborg. However, neither of them told Kouji and Shiro he was alive because Kenzo was going to build a Humongous Mecha to repel the Mykene invasion they predicted, and train its pilot. And both his father and he wanted to shield Kouji and Shiro from danger and psychological shock. It was not a bad reason, even if it was somewhat weak because Juzo was also building another Humongous Mecha and he raised them, even if he hired a maid because he was nearly always absent. When Kenzo revealed the truth to his little son, it took a long while for Shiro forgiving him. Though Kouji forgave him right away.
It is subverted with Kouji and Shiro's mother. In episode 90 from Mazinger Z, their mother appeared in the Institute, revealing she was alive and asking meeting her sons before telling them why she let them believe she was dead during years. Shiro was happy of getting his mother back, but Kouji was distrustful. It turned out that Kouji was right. Their mother was truly dead and that woman was a cyborg had fabricated Dr. Hell to infiltrate in the Institute and destroying Mazinger from within. So her "good reason for abandoning them" was false.
Its sequel was even darker. Great Mazinger dealt with themes such like racism and parental abandonment, the main character was a Deconstruction of the archetype that Kouji introduced, the Tsundere had mood shifts due to mental issues that had little to do with Tetsuya, The Professor was a very questionable father figure and mentor...
Darkest Hour: Its Darkest Hour happened in episode 92, but the Mazinger vs Great General of Darkness expanded upon it and turned it even more tragic: The army of Mykene Empire struck, easily razing several big cities (Londo, New York, Moscow...) to ruins. When they raided Tokyo, Kouji flew to fight them... and got the crap beaten out of him. When he returned to the Institute, he found out several Mykene Beasts had smashed the place, destroying Sayaka and Boss's Humongous Mecha. And Shiro, his little brother, had been hurt when a ceiling collapsed, and he urgently needed a blood transfusion. In spite of he was weak -and he was underage- Kouji DID demand they used his blood. Later, at the night, he was sitting in what was left of his bedroom, observing a picture of his father and his grandfather and crying Manly Tears as he muttered the Mykene Beasts would return, and he could not win, but he would fight even though he knew he was going to die (unbeknownst to him, sayaka was observing him, shedding tears as she heard him talking).
Deadly Gas: When Kouji and a Mechanical Beast fought near the crater of a volcano, toxic volcanic fumes pervaded the atmosphere (and unlike other examples of this trope, those fumes had a greyish color). Given that the Home Base of the heroes was located on Mount Fuji, it happened more often than you would expect. One example happened in episode 19: Kouji is engaged in aerial battle with a Mechanical Beast -Debira X-1-. During the fight they fly over Mount Fuji, and Kouji's visibility gets hindered by the dense curtain of poisonous gas rises from the crater.
Deflector Shields: The Photon Atomic Power Research Institute was equipped with deflective, energy barriers that surrounded the whole building to repel the strikes of the Monster of the Week and raids of enemy ships and airships. Unfortunately, a strong enough Kikaijuu could shatter the barrier by employing enough brute force, and The Dragon was smart enough to search and blow up the devices that made the barrier working.
Kouji Kabuto is always HotBlooded. That is nearly the only thing all his versions have in common. In the anime series, Kouji was an arrogant, sexist Jerk with a Heart of Gold and a Chaste Hero. However in the original manga he was less of a sexist and less of a jerk. He was more tactful, nicer -mainly to Sayaka- and was a bigger pervert (and he even blushed when Sayaka paid him a compliment). The Gosaku Ota manga, being an adaptation of the anime, stood halfway between both characterizations. Maybe the most weirdest version of all is the one from New Mazinger: he is a soldier lives in a post-apocalyptic, torn-war Crapsack World. He has noHot-Blooded Sideburns and his hair is partially red. He is only known as "Major Kabuto" and no version of Sayaka, Boss, Prof. Yumi or Dr. Hell show up (then again, it was only an one-shot story). The Z Mazinger Kouji Kabuto is more recognizable, but he has flashes of being a Totally Radical kind of teenager.
Sayaka Yumi was always a Tsundere, but in the original manga she was Type B and in the original series she was Type A. Her characterization in later versions varies between one type or another.
Dr. Kabuto in the original manga was a Large HamMad Scientist with an evil-looking scar running across the left side of his face. He had never met Dr. Hell and built Mazinger-Z because he felt guilty of his grandchildren were parentless and he wanted to give them something to protect themselves (and he told Kouji he would be able to take over the world using Mazinger-Z). In the anime version he was a well-meaning, average-looking, kind scientist built Mazinger-Z to fight back the menace of Dr. Hell. The Gosaku Ota manga version uses that characterization, but later retellings usually use the original Go Nagai version. In Shin Mazinger he is a Crazy AwesomeMad Scientist. In Shin Mazinger Zero... he is a monster.
Baron Ashura usually was completely loyal to Dr. Hell. But in the Gosaku Ota episodes he got fed up with Hell punishing his/her failures and Brocken mocking him/her, and he/she decided betraying Hell. In that storyline Ashura almost succeeded where Hell had failed.
Destructive Saviour: This trope was played for tragedy. As soon as the first episode we could see how destructive Mazinger-Z may be (in the original manga, Kouji destroyed half the cityas he was trying to figure out how to handle the damned machine. In the anime series he activated Mazinger on an unpopulated area; still, he destroyed his grandfather's lab, went on a rampage through the landscape and nearly got his little brother killed). When Kouji and Sayaka battle a Mechanical Beast, usually there is not much left of the battlefield in the wake of the fight. And when it is a city, buildings crumble down and people dies. As soon as the episode 7 it was shown people did NOT appreciate this and as far as they were concerned, Mazinger-Z was just as bad as Dr. Hell's Mechnical Beasts.
Detachment Combat: Several of the giant robots fought by Mazinger Z had this ability: Deimos F3, Velgas V5 (its parts had individual rocket propulsion and could attack separately), and a third one. Mazinger Z itself and one of its successors, Mazinkaiser, also did it sometimes (detaching theScrander Jet/Scrander Kaiser off themselves. Moreover, Mazinkaiser used its wings like a cutting, oversized boomerang).
Determinator: Kouji never gives up. Not even when he is going against several Kikaiju at once. Not even when the Robeast is completely impervious to his Humongous Mecha's attacks. Not even when it has abilities his robot could not match (he faced submarine and flying Kikaiju long before Mazinger got upgraded to be able to fly or swim or got weapons worked under water or in air). Not even when he is buried under rubble. Not even when he gets dumped into a freaking volcano! Not matter the odds, he will think fast, analyze his foe (and its weapons and capabilities), come up with a plan or cheat like crazy.
Geez, not even when he KNOWS the fight is utterly hopeless and there is no way to win he will quit. In the last episode of Mazinger Z and in the movie Mazinger Z tai Ankoku Daishogun he deployed Mazinger Z as stating he was not walking alive out of that battle and he knew that... but he did not care.
The only way you can get him stopping to fight is holding someone hostage. And even then he will try to exploit any edge to release the hostage and giving you a sound trashing.
Determined Defeatist: Kouji kept fighting even when he thought -or knew- that he couldn't win. He fought Jinray S1 despite of having almost no chances to defeat a flying, ultra-fast Robeast that used hit-and-run tactics. And he deployed Mazinger-Z to fight a squad of Mykene War Beasts even knowing that he'd not win that battle.
Determined Expression: Mazinger-Z is famous for being able to adopt this expression at will (remarkable feat in a robot without movile facial features) through subtle (for the 1970's) camera angles.
Despair Event Horizon: Kouji almost, almost crossed it during the Mazinger-Z vs Great General of Darkness movie. After several Mykene Warrior Monsters have easily destroyed four major cities (Paris, London, New York and Moscow) they strike Tokyo. He launches Mazinger-Z to fight them... and he barely walks out of it alive. The Warrior Monsters easily rip his mecha apart and turn Tokyo into burning ruins as he is unable make anything to stop them. Back in the Home Base, he learns MORE Warrior Monsters have visited while he was away. His Home Base is in ruins, Sayaka and Boss' Humongous Mechas have been destroyed, and worst of all, his little brother Shirou got hurt cause a collapsing ceiling and is in coma. Later, Kouji was sitting on -the remains of- his room, and he cried as he said he knew he could not win and he was going to die in the next battle; poor Sayaka, who was eavesdropping, also cried as hearing him.
It was way, WAY worse in one of the first chapters of Shin Mazinger Zero, where he did fully cross it. Straight after seeing his grandfather murdering his father and murdering Sayaka after raping her, and losing one of his arms he was thrust in Mazinger-Z and his body absorbed by the machine. Turned into a raging The Berserker, he began fighting Mechanical Beasts in spite of he not even knew what they were or whence they came, and his negative emotions -pain, rage, despair, sadness, loneliness- fed Mazinger-Z until its sleeping consciousness woke up, transformed into an Eldritch Abomination by poor Kouji's despair, and it burnt the world to ashes.
Dick Dastardly Stops to Cheat: In one of the Gosaku Ota manga chapters, Dr. Hell plots the next scheme: overwhelm Mazinger-Z with a Macross Missile Massacre as another of his Mechanical Beasts -Deathcross V9- attacks him, and as the Humongous Mecha is weakened and disoriented by the constant battering of missiles and the onslaught of the Beast, shooting a freaking huge missile to finish him off. It was a good plan. It could have even worked... Should Baron Ashura and Count Brocken have worked together. However, they were so eager and impatient for upstaging each other they attacked separately. Brocken shot the big missile without waiting for Ashura -wasting it and forcing them to rebuild the strategy-, and Ashura decided he could use that chance to defeat Mazinger-Z using the Mechanical Beast (because that tactic had worked so well in the past, right?) and humilliate Brocken.
Did You Die?: In episode 91, Kouji tries to bring a severely beaten Boss around. Boss mutters he is dead, and Kouji remindes him dead people can not speak. Boss realizes he is right and stands up.
Disappeared Dad: Kouji and Shiro. They were missing their father after he died in a lab experiment gone wrong. Years later they found out he was not dead. And shortly after they found about it, got used to the idea and got over their abandonment issues he died. For real this time.
Sayaka Yumi belongs to the "her father is physically present but he is barely there" category. Her father was Married to the Job, and getting the responsibility of saving the world dumped on his lap has not improved the situation. At least he tries to take care of Sayaka, but she knows his family is secondary to his job in the Institute, and she feels neglected.
Yuri, Sayaka's cousin. The main reason of she developed a demanding-attention, cranky attitude was her parents were always away, leaving her alone constantly.
Hiroshi, son of Dr. Kasuya, a scientist worked in the Institute. His father disappeared in a car crash, but the body was not found. He refused to accept his father was dead. How it turned out, he was right.
Disguised in Drag: Done by -of all people!- Baron Ashura at least twice (in episodes 7 and 36). He/she disguised like a woman to manipulate a mob or frighten nosy people away one of his/her operations. Fortunately he/she was a shape-shifter, so it was not so hard looking like a woman how it would be to him/her (on the grounds of Ashura being half-male, half-female). It overlapped with Creepy Crossdresser since it was pretty squicky -and eerie-.
Disposable Woman: Rumi was the maid Prof. Kabuto had hired to take care of his grandsons while he was creating Mazinger Z. She was cold-bloodly murdered by Baron Ashura less than five minutes after her first appearance. Kouji and Shiro cried when they found the corpse, but she was not mentioned again after the first episode.
Distaff Counterpart: Aphrodite A and Diana A; Minerva X is a greater example, since it is quite literally a feminine version of Mazinger.
Distracted by the Sexy: It happened fairly often in the manga. Usually was Sayaka the one did the -unwilling- distraction -either because her clothes were torn or because she was involuntarily naked-, but sometimes it was done by enemies to distract Kouji. The Gamia sisters come to mind...
Do-Anything Robot: Mazinger Z has weapons to solve nearly any situation it can find (although it helps Mazinger is piloted by a quick-thinking Genius Ditz who is capable of devising new strategies -or ways to get himself out of trouble- on the fly), and throughout the series it gets upgraded and equipped to combat at any environment.
Do Not Do This Cool Thing: Throughout the entire Mazinger trilogy and alternateseriesGo Nagai tried to send the message of War Is Hell. Cities were destroyed and burnt to ashes, innocent people were hurt and suffered, died in horrible ways (there are several instances of genocide), lost their loved ones, were enslaved or brainwashed... and victory always had a high prize. Unfortunately, he did so by showing really cool battles between colorful and awesome Humongous Mechas and impressive, imaginative monsters duking it out with spectacular Weapons Of Mass Destruction, so a lot of viewers kind of missed the point.
Do Not Touch the Funnel Cloud: Played more or less straight in Mazinkaiser. One of its weapons is Rust Tornado. Mazinkaiser blews three tornadoes from its grill mouth. Of course, anything it touches gets obliterated, and the wind gales kick big dirt clouds and leave a trail of destruction in its wake (in the movie it dug a wiiiiide trench across Mount Fuji). Though the area surrounding the attack does not seem so affected how it should.
The Dog Shot First: Inverted. In the Mazinkaiser OVA, Doctor Hell dies because his base exploded while he was trying to escape. When Go Nagai penned the Mazinkaiser manga, Kouji shoots him in an abrupt, albeit iconic and stylized, sequence.
Doing In the Wizard: In the Mazinger versus Great General of Darkness, a prophet warns Boss and his gang -and later Kouji and his friends- about the inminent Mykene invasion. It turns out that in reality he was Prof. Kenzo Kabuto, father of Kouji and Shiro, who kenw about the Mykene for reasons have nothing to do with prophecies.
And in the episode 36 of Mazinger Z, Baron Ashura pretended being a witch.
Do Not Adjust Your Set: Done as soon as the SECOND episode, when Baron Ashura announced the world belonged to Dr. Hell henceforth and all who opposed to him (i. e.: Mazinger-Z and the Photonic Research Institute) would be destroyed. Since then it was often employed by Dr. Hell and Baron Ashura to threaten, make demands, blackmail the Japanese Government, spreading lies and misinformation about the heroes and -successfully- scare people away in making their biding. In Great Mazinger, Great Marshall Of Hell was the only Mykene commander broadcast his demands by TV, showing Dr. Hell did not lose that custom even after dying and being brought back to life.
The Mazinger-Z versus Great General of Darkness is an alternate version of the final episode. So that watchers knew that Kouji Kabuto would be defeated and Mazinger-Z would be destroyed by the Mykene, but Tetsuya Tsurugiwould show up and crush the Mykene War Beasts.
Shin Mazinger Zero is a Stealth Sequel of the original series. So what readers knew what, even though Kouji defeated Dr. Hell for good, the Mykene Empire would rise afterwards. And when a foreteller tried to warn Kouji about it, everyone knew that he was his father Kenzo disguised. And everyone knew what would happen when Kouji fought the Mykene War Beasts.
Doomsday Device: Several of them. Dr. Hell -and sometimes Ashura- loved to build them (and in the manga of Gosaku Ota, he stated he was already working on them when he was working for Hitler, but he kept them for himself. He also claimed if he had revealed all his inventions, Germany would have won the war).
Downer Ending: The original series ended with Kouji killing Dr. Hell. However, the Mykene Empire -that had been awaiting for one of their enemies destroying the other- struck inmediately, razing to rubble several major cities -New York, London, Paris, Moscow and Tokyo-, bringing down the Photon Power Research Institute, destroying Diana-A, Boss Borot and Mazinger-Z itself. Kouji almost died, and he was saved by Tetsuya Tesurugi pulling off a Big Damn Heroes moment with Great Mazinger. The series ended with the humanity on the brink of being wiped out as several characters told Mazinger-Z was now useless. And later, in Great Mazinger, Dr. Hell returned, showing Kouji's efforts and struggle had been all for nothing. It was even worse in several retelling of the series:
In Shin Mazinger even though Kouji kills Dr. Hell and saves the day, it turned out to be a Batman Gambit by Baron Ashura, ensuring the Mikene Empire will rise and the series ends with Mazinger-Z defeated, the God Scrander destroyed!
Dragon with an Agenda: Gorgon. Supposedly he allied himself with Dr. Hell, but in reality he only was biding his time for betraying him, getting him killed ( He literally backstabbed him in the Gosaku Ota manga), and destroying Mazinger Z. He succeeded on all fronts.
Dramatic Sit-Down: The Hero Kouji did this in the Mazinger-Z vs. Great General of Darkness movie. Tokyo is attacked by Mykene Warrior Monsters, so he launches Mazinger-Z to fight them... and loses. Badly. Tokyo and his mecha are easily destroyed. It worse when he learns that his Home Base is in ruins and Love Interest Sayaka and Boss' Humongous Mechas have been destroyed by more monsters. His little brother Shirou was put in a coma after a ceiling collapsed on him. Kouji was sitting in his (destroyed) room and cried. He started talking to himself and that he knew he couldn't win the next battle and would die because of it; Sayaka, who was eavesdropping, was driven to tears by this.
The first happened in an early episode, when Ashura, disheartened after still another defeat, thought the only way to redeem himself/herself to Hell's eyes was by comitting suicide. Hell rebuked that was dumb, and the way to atone for his/her failures was going on fighting until destroying their enemy.
The second time happened in episode 39, when he was so badly frightened on the possibility of Count Brocken replacing him that he staked his life on his next operation. When he failed, Brocken was all but ordering him killing himself, and he was about to do it when Hell stopped him, stating that even if he had failed in destroying Mazinger-Z, his war tactics had delivered a huge blow to Japan, and he forgave him.
The third -and final- time happened in episode 78. Ashura was so sick of being defeated, mocked and scorned by enemies and allies alike he hijacked the flying fortress Ghoul to crash it against the Institute in a Taking You with Me tactic. He failed, but he died believing he had finally won.
Drives Like Crazy: Koji is a not a bad driver. Oh, no. In fact, when he drives he is the only person on the road that is absolutely safe. He is a Badass Biker who believes traffic regulations are mere suggestions, speed limits are a myth and bikes were made to pull crazy stunts with them.
Dug Too Deep: An archaelogical expedition researching ancient ruins in the Greek Island of Bardos went too deep in the underground mazes of the island and found an army of Humongous Mecha. Subverted, since Dr. Hell hoped finding them and using them to further his goals. Also, when Hell seized those robots, he drew the attention of the Mykene Empire -an ancient civilization had been forced to live underground- and they decided return to the surface quite violently.
Dr. Kabuto's lab basement also counts. It was hilariously lampshaded by Kouji in the original manga (since Kabuto had built Mazinger in his home in the middle of a city instead of in his mansion located in Mount Fuji), when he found the entrance and asked: "Since when is there a basement in the garden?"
God Mazinger: Princess Aira, who ruled the kingdom of Mu alongside her father.
New Mazinger: Princess Krishna a Distressed Damsel Major Kabuto met when he was accidentally thrown in another dimension. She was trying to keep her kingdom together after her father got murdered in an ambush.
Evil Is Not a Toy: A textbook example. Dr.Hell searched and found the army of giant robots that legends rumored the lost civilization Mykene used, and thought he could control them through the rod of Rhode (a device he invented) and use them to Take Over the World. However, the Mykene civilization still existed, thriving underground... and Dr. Hell stealing their ancient weapons drew their attention back to the surface. Oops. One of them- Archduke Gorgon- confronted Hell, accusing him of stealing their Lost Technology and demanding that he returned it. Hell tried to bargain with him, and Gorgon pretended to agree, but in reality he planned to backstab Hell as soon as possible -which he did- to allow the Mykene Empire to conquer the surface world instead of Hell.
Eye Scream: In the Mazinger vs Great General of Darkness, Kouji shot Mazinger's drilling missiles right in the eye of a Mykene Warrior Beast. So the tiny missiles drilled through its eye and exploded inside its head. Ouch. And in another episode, Sayaka blew up with her Aphrodite-A Breast Missiles the only weak points of the Mechanical Beast Gumbina M5... its eyes. Double ouch.
Exactly What I Aimed At: In the Mazinkaiser movie, Tetsuya Tsurugi is fighting Angoras and Scarabeth, two commanders of the Mykene 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 -Mykene 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.
Face Ship: There was a beastly face built on the frontside of Guru. On the top of Bood there was a head built in.
Faceless Goons: Ninety percent of the Mooks wore uniform concealed his faces. The Iron Masks wore a black suit, ancient armor and Greek-looking helmets fully hid their faces minus their mouth and chin. Subverted into a Nightmare Fuel fashion when one of them got their helmet removed and he was missing his skull's upper half, removed by the Big Bad when the mook was Reforged into a Minion. The purpose of those helmets is not to protect their heads but to replacing their skulls and protecting their brains. The Iron Crosses have identical uniforms, resembling modern-day soldiers, but they also seem identical and all of them also wear helmets covering his face up his mouth.
Falling into the Cockpit: Kouji knew absolutely nothing about piloting a giant robot -or any manner of robot, really- and in the first few episodes it shows. Mazinger went on a rampage the first time he activated it because he kept punching random buttons, and he got beaten in his first battles. Sayaka and her father did their best to teach him quickly, but until then he only survived due to Mazinger's impressive weaponry and sturdy body armor... and Kouji soon revealed he was a quick-thinker that could come up with new strategies on the fly.
Feather Flechettes: One of the attacks of Mechanical Beast Harpy π7 was hurling wave after wave of its metallic feathers at their enemies. Those feathers were hard and sharp enough to slice and cut through Japanium, and with they very nearly destroyed Mazinger-Z and destroyed Aphrodite-A for good.
Feed It a Bomb: Kouji and Sayaka use this strategy to defeat Mechanical Beast Dian N4. How do you defeat an enemy is geared with a nearly impervious armor? You shove a giant missile down its throat, of course!
Female Gaze: Kouji Kabuto. In the anime he was shown half-naked more often than Sayaka. And in the manga he visited a hot springs resort, and stripped himself once for not reason at all. Duke Fleed from UFO Robo Grendizer also "suffered" from it. An example was when Kouji went to Duke's room late in the night to discuss a matter was worrying him, and both of them were naked up waist during the conversation.
Festival Episode: Episode 29 happens during a festival that Kouji and his friends were participating on. Unfortunately, the appearance of Mechanical Beast Grengus C3 put a damper on the festivities.
Final Battle: It varies depending on if we are discussing the Go Nagai manga, the anime series or the Gosaku Ota manga, but it had two battles at the end of the series. At the final of the anime series, the main characters located Dr. Hell's Supervillain Lair at last. Quickly they began to make preparations for the final battle, but Hell used a last scheme to hinder them as he completed his own preparations. Mazinger-Z, Venus A and Boss Borot stormed Hell's Island, supported by the Japanese army, but Dr. Hell sent against them his last Mechanical Beasts. The three Humongous Mecha got severely trashed, but Mazinger-Z could still work. Kouji stormed the base, destroying and blowing up all what he saw. Hell set his Lair to self-destruct and he and Brocken tried to flee on the aerial fortress Guru. However, Mazinger-Z chased them and they faced off for last time on an aerial battle over the ocean. It was subverted, though, since all of it happened in the second-to-last episode, and the narration -and the scenes involving a smug Gorgon- warned the last episode would be NOT a happy day. The events were very different on the Go Nagai manga (Hell attacked first, deploying several dozens of Mechanical Beasts at once to invade Japan. Ashura and Brocken coordinated their squads in the assault, and the Japanese army used Mass-Production Mazingers against Hell. Finally, Kouji and Sayaka fought alone against the Island of Hell, what had transformed into a humongous Humongous Mecha). The Gosaku Ota episodes are similar to the anime, but Gorgon makes his move while Kouji is storming the base. He goads his Warrior Monsters against Mazinger-Z and backstabs Hell when he is distracted before leaving the base. Enraged and dying, Hell pulls a lever. Hell's Island takes off and flies towards the Institute to crash on it. However, Great Mazinger arrives, defeats the Mykene Beasts, fetches a defeated Mazinger-Z and runs away with it. Meanwhile, the battle has altered the course of the island, and it floats upwards, leaving the atmosphere and losing itself in the space...
Several Mechanical Beasts were armed with this weapon (for example, Danchel in one of the earlier episodes. Or one Beast from the Mazinger-Z vs Devilman feature).
Finishing Move: A bit of a subversion. Breast Fire and Rust Hurricane would be Mazinger-Z Finishing Moves. However, Kouji used whatever weapon he saw fit to end up the battle. In the original manga, Kouji mainly used Mazinger-Z's fists and kicks to beat the enemy and then he finished it off with whatever weapon.
First Episode Spoiler: Kouji's grandfather gets assassinated in the first episode. Shortly before dying he reveals to his grandsons that he was secretly building a Humongous Mecha.
First Girl Wins: Sayaka was the first girl introduced in the series, and Love Interest of The Hero Kouji Kabuto. In the anime she was the second female character introduced, though, but she was the first girl introduced that was a potential couple for Kouji (unlike Rumi who was an adult woman and was, well, dead).
First Kiss: In the Mazinger-Z vs Great General of Darkness, Kouji is going to sortie with Mazinger-Z when Sayaka stops him. He is on the brink of crossing the Despair Event Horizon, and believing he'll inevitably die in the next battle, and Sayaka is anguished about it. They look at each other for a long moment, but finally they broke up without kissing. However, when that scene was replayed in the manga (the episodes written by Gosaku Ota), they DID kiss. That scene was very heartwarming, but their relationship after the kiss was awkward for a while (since Kouji did now know how dealing with they being an Official Couple).
Fish People: The Chip Kamoy ("divine fishes" in Ainu idiom). They showed up in Gosaku Ota manga version, and they were a race from gigantic, bipedal, humanoid maneater fishes from another dimension raised herds of humans like if they were cattle. Their bodies were scaly and filled with fins. However they had depleted their homeworld's natural resources and were running out of food, so they crossed over to our dimension to find more preys.
The Evil Genius: Archduke Gorgon. On the surface he would seem The Brute, but in reality he was a manipulative, conniving, scheming, Magnificent Bastard prefered using his intelligence before his -considerable- physical strength- and provided the Big Bad with increasingly powerful weapons.
The Brute: Count Brocken. Although he is not so physically powerful like Gorgon, he commanded his own corps and would often rather using strength instead of cunning. He is an ex-Nazi officer, so he definitely liked getting his hands dirty.
The Dark Chick: Viscount Pygman. He was not a girl but he definitelystood out and he definitely was considered a freak. His skills, abilities and powers were also very different of his colleagues' ones.
Flat "What.": In a chapter of Shin Mazinger Zero, Kouji and Minerva-X are together inside the cockpit. During the battle Minerva lands on Kouji on a very awkward and embarassing position. Sayaka -who has just arrived and destroyed three Mechanical beasts in a fit of jealous rage- sees him, and they -after displayin a tremendously comical Oh Crap! stares- try to explain it is not what it seems, and Minerva is not human but she actually is a Super Robo created by The Professor Dr. Kabuto to be Mazinger-Z's partner. Sayaka's reaction?
Flying Brick: Mazinger Z after its MidSeasonUpgrade, but also several Kikaiju. one of the worst offenders was Jinray S1 (It flew at Match-5 speed when Mazinger could not fly yet, it threw bolts of lightning, and shot missiles)
Follow the Leader: Super Robot Genre shows like Tetsujin 28 already had their own success, but it was Mazinger Z that solidified the concept of piloting a robot (via a cockpit within its head, rather than remote control) and started a revolutionary trend that attracted toy makers and captivated children. Such influence would eventually lead to all sorts of landmark works that keep said genre alive and relevant to this day.
Franchise Zombie: The original anime series was supposed to wrap up at episode 57. However, the series was so wildly succesfull it was continued for other thirty-five episodes. And then two movies were made. And two sequels. And more movies. And crossovers. And spin-offs. And reboots. And remakes. And Go Nagai has stated he has got offers for a Mazinger-Z live-action movie... Tropes Are Not Bad however as the series is still popular and Mazinger makes appearances to this day.
Friend on the Force: Inspector Yamitaro Ankokuji, which appeared in the first episode of the original manga and aided the good guys for some chapters.
Forgotten Phlebotinum: It was played straight often. Many times Dr. Hell came up with a Mechanical Beast equiped with a weapon put Kouji or Mazinger-Z in a serious disadvantage: Gromazen R9 shot an acid could melt Aphrodite A's armor (that was made of Japanium, although it was less tough than Mazinger Z's), Kingdan X10 projected mirages, Holzon V3 set eathquakes off, Jinray S1 flew at Match 5, Aeros B2 could absorb Mazinger's attacks and hurling them back, Desma A1 caused hallucinations, Gumbina M5 was nearly invulnerable... and they were not used again. However, sometimes Dr. Hell reused and improved some strategies or weapons, or deceived the enemy in believing he was using the same trick.
Forgotten Superweapon: In episode 10 Mazinger-Z shot missiles from its fingers. That weapon never showed up again. It is somewhat subverted, though, since it was not so useful and Mazinger-Z had better and more powerful weapons, so it is likelier than the animators realized it was silly placing missiles in the fingers of a Rocket Punch, and they chose to forget about it and replace them with weapons were not Awesome, but Impractical.
Freeze Ray: one of the weapons of Mazinger Z: its helmet's horns shoot freezing beams tat turn the enemy into a chunk of frozen, brittle ice. It is called REITOU BEAM!!!
Freudian Excuse: Dr. Hell was an a unwanted child -a fact his mother took great pains to remind him of constantly-. When he was a school student, he was constantly belittled by professors (who believed it was impossible he got those marks without cheating) and beaten by his schoolmates. When he was in college, he took pride on his grades... and then a foreign student (Juzo Kabuto, Kouji's Grandfather) surpassed him easily before wooing the woman he was in love with. After saving a little girl and being beaten up by her father (since he falsely believed he was molesting her), he declared he was sick of it all and one day everybody would kneel to him. And then Nazism happened and he... got tips.
From Bad to Worse: In the beginning of the Mazinger-Z versus Great General of Darkness feature, Kouji believes his life will be peaceful from now on. Then an unknown army of Robeasts razes the main cities of the world to ashes. After that, they strike Tokyo. Kouji goes to fight them... and he gets easily defeated. The War Beasts easily burn Tokyo to ashes and leave after tearing Mazinger-Z apart. When he returns to his Home Base, he finds the place has been turned in ruins for another squad of Beasts, his friends have been hurt and their Humongous Mecha destroyed... and his little brother got crushed by a failing ceiling and is in coma. Shortly after more Beasts attack the Institute and he goes to fight them, fully believing he will die. He gets soundly beaten, and Mazinger-Z is finally destroyed. The only highlight is he manages walking out of alive.