The Legend of the Overfiend

AKA Choujin Densetsu Urotsukidouji or The Legend of the Overfiend.

A series of horror hentai anime/manga, created by Toshio Maeda. Trope Codifier of the Naughty Tentacles genre. An unfortunately popular candidate for being unwittingly placed in or around the kids section of DVD stores and libraries.

There are six installments of the Anime version, all of them OVA:

 * Choujin Densetsu Urotsukidouji (Legend of the Overfiend, 1987-1989). Total uncut length: 2:26:06.
 * Shin Choujin Densetsu Urotsukidouji: Mataiden (Legend of the Demon Womb, 1990-1991). Total uncut length: 1:37:33.
 * Choujin Densetsu Urotsukidouji: Mirai Hen (Return of the Overfiend, 1992-1993).
 * Choujin Densetsu Urotsukidouji: Hourou Hen (Inferno Road, 1993-1995).
 * Choujin Densetsu Urotsukidouji: Kanketsu Hen (Urotsukidouji V: The Final Chapter, 1996). Was never completed.
 * The Urotsuki, aka Urotsukidouji: New Saga (2002): A modern retelling of the first half of Legend of the Overfiend.

This Anime Provides examples of:

 * Abusive Parents: Niki's.
 * After the End: The series setting after the second episode.
 * All Anime Is Naughty Tentacles: Due to frequently being placed in children's sections by mistake, there's a good chance this is the series that caused the trope.
 * Anti-Hero: Amano Jyaku.
 * Anti-Villain: Suikakajyu.
 * Black and Black Morality: Caesar and the Makemonos in Return. The other factions are not much better.
 * Body Horror
 * Caught with Your Pants Down: Nagumo is caught by the school jock Ozaki masturbating in the ball pit, he then holds him up by the back of his shirt and shows the entire student body his erection.
 * Coitus Uninterruptus: In Legend of the Demon Womb, Amano Jyaku holds a long conversation while having sex with Mimi. In a lava pool.
 * Crapsack World: It was a pretty harsh world to live in even before the Endofthe World As We Know It. The rampaging demons and bloodthirsty cults that came after didn't help things.
 * Cut Short: Urotsukidouji: New Saga was a retelling of the original Legend of the Overfiend but the project was cut short three episodes in, leaving a ton of unresolved plot points and inconsistent characterisation. Even Amano Jyaku was practically a nonentity.
 * Darker and Edgier: Every installment compared to the one before. Most notable between Demon Womb and Return.
 * Deadly Upgrade: Anyone who tastes the Chojin's blood (or other bodily fluids) gets a portion of its power, until that power overwhelms and kills them after a few hours or days.
 * Deal with the Devil: Niki. He resorts to killing his abusive parents, and replacing his penis with a demon phallus (with some nasty DIY surgery), all because the demons promise him the power to steal Akemi from Nagumo.
 * Decoy Protagonist: Ozaki. Although he's introduced as the jock that the other protagonist, Amamo, has his eyes on, he bites it after his first fight. The nerdy kid that was in the beginning? He's the actual protagonist. Well, asides from Amamo.
 * Deus Angst Machina: Niki, again. He's a friendless loser, rejected by his love interest, women call him a dickless wonder, his father beats him while his mother cheers his father on.
 * Earth Is Young: the world is only three thousand years old. Uses the Type A (lack of) justification. The world is simply stated to be young, and this is never discussed. The intro of the movie version also have an indirect hint of Type B: Mankind is scolded for being so ignorant and foolish that they don't even know about parallel universes, so one can expect that people are supposed to simply shut up about their silly little theories about the origins of the universe.
 * The End of the World as We Know It: Happens at the end of Legend of the Overfiend, and the Overfiend keeps threatening to bring about an even more thorough end to the After the End setting of the sequels.
 * Evil Laugh: Münchhausen does this a lot in Legend of the Demon Womb, to the point of Narm.
 * Fantastic Racism:Caesar displays this toward the Makemono, herding them into concentration camps and generally regarding them as depraved beasts (not without justification, in many a case).
 * Fan Disservice: To- you know-- normal people.
 * Getting Crap Past the Radar: This series (and pretty much the entire naughty tentacles hentai genre) was conceived predominantly to get around the strict ban in Japan on depictions of genitalia. Those are totally tentacles and not penises...
 * God Is Evil: Once the fully awakened Nagumo begins destroying cities and shattering the dimensional barriers, Amano and his people realize that maybe their prophecies of the Chojin delivering Paradise were mistaken.
 * Gorn: Apparently, a woman being raped so hard she explodes in a shower of blood and intestines is erotic to some people.
 * Grey and Gray Morality: Few of the characters are purely black or white. Even Amano Jyaku's archenemy Suikakajyu was trying to protect the three worlds all along. Later on the characters have to side with either the Chojin, a Knight Templar deity at best, or his allegedly evil counterpart, reborn as a young girl. It's not clear to them or the audience which one humanity would be worse off with.
 * The Grunting Orgasm: Every time the Chojin scores rapes a girl.
 * Hooker with a Heart of Gold: Megumi Amano. Not literally a hooker, but otherwise follows the trope to the T.
 * Hopeless Suitor: Niki in Legend of the Overfiend, whose unrequited love for Akemi drives him to.
 * In the Blood: In the most literal sense. A transfusion of Nagumo's blood (or sperm) will transform the recipient into a monster.
 * Kaiju: The giant demon-thing Nagumo turns into to destroy the world, the giant sea demon the Makai prince summons to try to fight him, and several other giant monsters conjured up by different factions against one another.
 * The Legions of Hell.
 * Kick the Dog: Niki's parents beat and humiliate him shortly before they die. Münchhausen's teacher and principal beat and humiliate him right before they die. Ozaki publicly humiliates Nagumo right before he dies. Let's just say dogs are very well-protected in the Urotsukidouji universe.
 * Love Triangle: Akemi, Nagumo and Niki.
 * Murder the Hypotenuse: Niki tries to literally do this to Nagumo. Doesn't work; since Nagumo's the father of the Chojin and he just comes back to life.
 * Naughty Tentacles. They've been around since about 1820 (see Dreams of the Fisherman's Wife at The Other Wiki), but, without a doubt, the modern Trope Codifier.
 * Negative Continuity: By the end of Legend of the Overfiend, the three realms have, as said prior, been all but destroyed by Nagumo. But in the next instalment, Demon Womb, everything's fine again, without explanation. Could be explained as an Interquel, as the third episode then proceeds from the world's destruction.
 * Nuke'Em: Münchhausen plans to destroy the Chojin by launching a whole fleet of ICBM's against Osaka. Amano stops them, not so much to save the Chojin as because a lot of innocent people have taken refuge there as well.
 * Ordinary High School Student: Nagumo; the lovesick nerd picked upon by the basketball jocks is a actually a monstrous being destined to father the god of gods and destroy the world so said god of gods can remake it.
 * Out with a Bang: Tons of times. Literally with a bang. Those poor women...
 * Your Head Asplode
 * Parental Incest: Caesar and his daughter Alector from Return of the Overfiend. Alector had little say in the matter...
 * Plot With Porn
 * Porn Names: The dub voice actors were so disgusted with the frequent sex and rape they used fake names that sounded like the names porn stars would use.
 * Prophetic Fallacy: A prophecy claims that the Chojin will bring about a glorious new world once the apocalyptic smoke clears. The heroes begin to seriously doubt that as the series goes on, and it ended without ever revealing how much, if any, truth there was to the prophecy.
 * Red Herring: Popular school jock Ozaki is presented as the obvious incarnation of the Chojin, though Genre Savvy viewers will probably see through it the moment they find out there's a shy, lovesick nerd in the running too. A more effective red herring is that.
 * Shoot the Shaggy Dog: Legend of the Overfiend. Think about it. Amano and the Makai spend the whole time trying to find the Chojin and sparring with each other; but in the end Nagumo just turns into the destructor when he has sex and destroys the world. Nothing that either Amano or the Makai did really had any effect on anything; the world would still be destroyed if they had done nothing. (Assuming that despite the events of saga not occurring Nagumo did eventually have sex at some point in his life...)
 * Refuge in Audacity: There's something utterly ridiculous about being raped by a demon and exploding.
 * Shrouded in Myth: Amano's expecting the Chojin's human incarnation to be a powerful, charismatic figure, since his culture basically worships the Chojin. Ironically, his sister Megumi had the answer right all along (at least, she kinda did).
 * Stupid Jetpack Hitler: He commissioned a demon-summoning rape machine this time around.
 * Super-Powered Evil Side: Nagumo. And Niki. And Takeaki.
 * Those Wacky Nazis
 * The Tokyo Fireball: Happens all the time.
 * Utopia Justifies the Means: The Chojin's justification for destroying the three worlds.
 * Unbuilt Trope: For Naughty Tentacles. Yes, really. In the original movie, being raped by tentacles was generally not particularly erotic, as it almost always led to the tentacles tearing the person apart from the inside. They were used primarily for horror effect, not titillation.
 * Well-Intentioned Extremist: Suikakajyu. He resorts to extreme lengths to prevent the Chojin being born (even causing the Great Kanto Earthquake of 1923). By the end of the movie, we find out his actions were justified.
 * What Do You Mean It's Not Symbolic?: Many a film critic has tried explaining this one in terms of Freudian symbolism, Japanese sociological issues, and the legacy of the Hiroshima/Nagasaki bombings. Sooner or later, they all give up.
 * What Do You Mean It's Not Symbolic?: Many a film critic has tried explaining this one in terms of Freudian symbolism, Japanese sociological issues, and the legacy of the Hiroshima/Nagasaki bombings. Sooner or later, they all give up.

Examples involving New Saga:

 * Naughty Tentacles: Used by Dorkakuryu