Orochi

The Yamata no Orochi is a eight-headed and eight-tailed serpentine monster in Japanese Mythology, similar in appearance to the Lernaean Hydra but with one less (or alternately, one more) head. According to Shinto legend, the Orochi was defeated by the storm god Susano-o, who answered a request for aid by two earthly deities who were forced by the Orochi to hand over one of their daughters every year to be devoured by the beast, and were now down to their eighth and last one, Princess Kushinada. Just to distinguish the tale from Western dragon slaying myths, Susano-o first lured the Orochi out by disguising himself as Kushinada, and then killed it by setting out a bowl of strong sake for each head, letting it drink itself into a stupor, then lopping them off. Inside Orochi's body Susano-o found the sword Ame-no-Murakumo-no-Tsurugi ("Sword of the Gathering Clouds of Heaven") that was later re-named "Kusanagi" ("Grass Cutter"), and is one of Japan's Three Sacred Treasures.

According to a wide assortment of Anime and video game series, the Orochi is alive and well and at large in present-day Japan. Sometimes it's literally Orochi, or anything from a Monster of the Week to a Big Bad with snake-themed powers. The trope holds pretty strong and is different than simply being associated with snakes; if your story has a Crystal Dragon Jesus, Orochi will be its Devil.

Anime and Manga

 * Ranma 1/2 had one that shared a personality almost identical to its mythological counterpart; when it stirred itself, it did little more than just wanting to eat women and drink booze. However, it appeared to have only seven heads.  This Orochi had magical moss growing on its main head that was a powerful curative- even drinking water that had flowed past the moss could sustain a person's life, as well as making animals grow to unnatural sizes. Notably, the male characters also had to dress in drag in order to lure it out (while Akane disguised herself as a boy to avoid it.) Unfortunately, they all looked so hideous the Orochi wasn't fooled.
 * Another spiritual example/reference is Happosai, a sake-swilling Dirty Old Man who goes into withdrawal if he is unable to sate his perversion and perhaps the most powerful martial artist in the series. In his Backstory, he was only beaten when his students left out enough sake for him to drink himself into a stupor, after which they sealed him in a cave with a bundle of dynamite by means of a Shimenawa-adorned boulder. He of course returns to bug Ranma, and finds himself thwarted time and time again by his intended victim - a Hot Blooded "Manly Man" acting as a perfect Susanoo figure, complete with an Attractive Bent Gender curse that Happosai always falls for.
 * Blue Seed. Unless you read the subtitles, which tend to mistranslate it as "Orochi no Orochi".
 * Kannazuki no Miko
 * One of the main villains of Naruto is Orochimaru, a rogue ninja with the ability to summon snakes (And oddly, the Kusanagi sword.) In this case, he's actually based on the character of the same name from the folktale Jiraiya Goketsu Monogatari (As are Jiraiya and Tsunade, of course). However, since the original Orochimaru was likely named after the Orochi, we'll keep him here.
 * Also, later on, Orochimaru briefly displays the ability to turn into one with a technique called Yamata no Jutsu. Shortly afterward,
 * Yu-Gi-Oh (Yamata Dragon, one of Noah's monster cards in the Virtual World Arc.)
 * Digimon Tamers has Orochimon, whose heads are armored, and each somewhat different. They grow back after being damaged by most attacks, too.
 * Inverted in that drinking sake made it stronger, not weaker.
 * There's also a Susanoomon. He also has a BFS, though - named Orochi. Sadly, he and Orochimon never met, and Susanoomon being an end-of-season super-duper mode and Orochimon being a mid-season Monster of the Week the previous year, they're not really in the same league.
 * In Shaman King, Bokuto no Ryu's In addition, one of Ryu's strongest attacks is his "Ame-No-Murakumo that slew Yamato-No-Orochi", which surrounds his wooden sword in cloud-like swirls of energy before slashing. A bit of a mix-up of the legend's particulars, but cool either way.
 * In Ayakashi Ayashi a main character just happens to be Orochi himself, and the fight with Susanoo is re-enacted in the end (well, more or less), with interesting results.
 * In Hell Teacher Nube, the most powerful Yokai of all (surpassing even Baki) is the great and terrifying Yamata No Orochi, whom a Mad Scientist summons from the netherworld using ancient technology and mystic rituals. It would have devastated all of Japan if not for Nube and his students' intervention.
 * The method by which it was dispatched is actually an awesome moment for the manga --.
 * Mugen Densetsu Takamagahara: Dream Saga, based on Japanese myth, has a chapter re-enacting the Orochi story.
 * In Sekirei, Tsukiumi has an attack called Yamata no Orochi
 * In the manga Tenjho Tenge, the story of Susanoo and Orochi is presented as a symbolic allegory for the story of the founding of the Gaoshiki clan, to which most of the characters in the series belong.
 * Akazukin Chacha and friends defeated a nine-headed snake who ate virgin girls by getting him drunk on sake.
 * One of the Childs of the Hi ME in Mai-HiME has "only" six heads but is otherwise modeled after the orochi.
 * The Yamata no Orochi dragon appears in the penultimate story arc in Yaiba. Is revealed that

Comic Books

 * In one Usagi Yojimbo arc, Grasscutter, the tale is told as the origin of the story of the sword Kusanagi.

Film

 * In Godzilla, Mothra, King Ghidorah: Giant Monsters All-Out Attack, King Ghidorah is alluded to be an immature Orochi-- having only grown 3 of his fated 8 heads.
 * Toho's 1994 movie Orochi: The Eight-Headed Dragon had a very chubby Orochi. It also bore an notable resemblance to Ghidorah, another Toho creation. The monster's model kit was sold by D-tech, though it is now sold out http://d-tech-pro.com/en/detail/D-0009.html
 * In Onmyouji II, the two chosen children, who are actually reincarnations of Susanoo and Amaterasu, are each marked with a four-headed serpent tattoo that combine to make the Mark of Orochi.

Tabletop Games

 * In Magic the Gathering's Kamigawa setting, the term 'orochi' refers to a race of forest-dwelling four-armed bipedal snake-people. O-Kagachi, the biggest and baddest of all spirits, is a take on Orochi proper.
 * In Legend of the Five Rings, Orochi are simple (one-headed) sea serpents.
 * The first appearance of the Yuan-Ti Anathema in Dungeons and Dragons 3rd Edition resembled a giant, multi-headed, vaguely humanoid snake.

Video Games

 * The King of Fighters (specifically, the 95 to 97 Arc) has the literal Orochi. In this series, he's a fanatical servant of Gaia who believes that Humans Are Bastards and considers the very beings that Gaia made a threat. Similarly to the myth, he is defeated by the Kusanagi, Yasakani, and Yata clans, who sealed him away. Unfortunately his influence spread to the Yasakani and they made a contract with him to gain power. This caused a civil war with their former allies, much to Orochi's glee. He's also got a cult of servants known as the Hakkesshu made up of a musical band, (Chris, Yashiro, Shermie) a Sinister Minister, (Goenitz) two sexy secretaries, (Mature and Vice) a homicidal maniac, (Ryuji Yamazaki) and the father (Guidel) of a hot soldier girl (Leona) who was killed by the Sinister Minister because he decided to bow out on Orochi's plan, and his plan is to gather enough energy so it can be fully revived and destroy humanity (alonside a back-up plan consisting on the ritual sacrifice of a Naive Everygirl who happens to be the reincarnation of Princess Kushinada). He doesn't make an actual appearance until '97, where he possesses Chris to act as the Final Boss (an Anticlimax Boss, given his predecessors). In the end, he is defeated by the Three Sacred Treasures. (Chizuru, Kyo and Iori) In a last-ditch effort, he tries to turn Iori against Kyo and Chizuru by stirring up Iori's half-Orochi blood and turning him into Orochi Iori. This fails, as Orochi Iori ensnares Orochi long enough for Kyo to deliver the deathblow (under approval of the spirit of Iori's ancestors, who regret what they've done), thus letting Kushinada's incarnation Yuki escape her destiny and giving Chizuru the chance to seal him away again and prevent The End of the World As We Know It. Orochi, on his death throes, decides to wait and observe humanity to see if they're truly deserving of his "judgment".
 * Whereas the second KOF saga (The NESTS Chronicles) had a plot that resembled a bad sci-fi movie, the third and current saga (The Tales of Ash, which started in 2003) seems to be sticking closer to the original Orochi Saga. Not only is there a Nebulous Evil Organization known as "Those From the Past" trying to undo the seal on Orochi, but the supposed "protagonist", Ash Crimson, is going around with the facade of a weak and unassuming fighter, only to pop up and steal the powers of Chizuru and Iori (as Orochi Iori, no less) at the end of 2003 and XI, leaving Kyo as the only remaining non-depowered descendant of the three clans that sealed Orochi. Of course, Ash has singled out Kyo as his final target.
 * Okami takes this trope even further by retelling the original legend, featuring the characters Susano (who deals the final blow to the monster) and Kushi (the woman who was to be sacrificed to it). It is a long, two-phase battle that involves force-feeding Orochi the legendary sake, then taking out its heads one by one, before Susano jumps in to deal the final blow. The player even receives their first sword/glaive as a prize from the battle, although it's not the Kusanagi blade. You get that from a different boss entirely.
 * When the same battle reoccurs in the past, Nagi is even dressed up in Nami's sacrificial robes.
 * Likewise, Golden Sun: The Lost Age has Susa and Kushinada who fill similar roles. You also get to keep the sword in this case.
 * Shin Megami Tensei. Orochi can usually become one of your Mons.
 * Hilariously, in Strange Journey (where the protagonist wears full-body-concealing armor), telling it you're a beautiful woman will cause Orochi to join instantly.
 * A loose reinterpretation of Orochi is the Big Bad of the game Warriors Orochi, where he's a demonic, humanoid Blood Knight with his own army.
 * The very premise of "Warriors Orochi" is that Orochi himself essentially got bored and squished Japan's Sengoku era and China's Three Kingdoms era together (represented by characters and areas from the "Samurai Warriors" and "Dynasty Warriors") in order to fight history's greatest warriors. Predictably, he's the final boss of every story mode in the first game and is rather difficult to beat. Although it takes a fair amount to unlock Orochi in the first game, you're able to play him right off the bat in the second. And in both he's still about as absurdly powerful when you're in command of the giant snake man with the funny hat as he is as a boss!
 * The portion of Dragon Quest III taking place in a Japanese Fantasy Counterpart Culture is a loose retelling of the Orochi myth, with your party in the place of Susanoo.
 * The same is true of the primary sidequest of the Japan-inspired village in Metal Saga. This is strange, as it's an After the End game.
 * In Gotcha Force, the green-haired main antagonist of the game was named Orochi.
 * Orochimaru is depicted as a pretty blue haired bishounen and one of the hero characters in the Tengai Makyou (Far East of Eden) games.
 * Also a Jiraiya Goketsu Monogatari reference, as his partners are Jiraiya (although spelled differently, as Ziria) and Tsunade.
 * In Bleach DS: Blade of Fate and its sequel Dark Souls, Yamata no Orochi is Head Captain Yamamoto's ultimate attack, consisting of sending a large snake-like pillar of fire straight upwards, which then comes back down as eight smaller streams. Subverting the trope, this character is actually a protagonist and ally.
 * Furthermore, his basic special attacks are all numbered heads. Useable are heads 1 through 5, though sound test data reveals there were heads 6 through 8 planned.
 * In Final Fantasy II's Soul of Rebirth mode in Final Fantasy I & II: Dawn of Souls, the Yamata no Orochi is available as an optional boss, as a Palette Swap of Tiamat.
 * The first Mega Man Zero game has the Guard Orotic, a Boss occupying a factory that La Résistance must take over. Two heads represent each of the three elements (fire, ice, lighting), while the last pair is non-elemental.
 * In Princess Tomato in The Salad Kingdom, the Orochi is actually a monster made of... bananas.
 * The Black Beast of Blaz Blue bears a heavy resemblance to Orochi in its appearance. It was created from The Murakumo Unit (ν-13), and defeated by the wielder of The Susanoo Unit (Hakumen).
 * Phase 0 reveals that  was engineered to be a sacrifice to the Black Beast to temporarily halt its rampage, making her a Kushinada figure. Oddly enough the one who rescued her from this fate is not the Susanoo figure. The original Bloodedge fought against the Black Beast to ensure that her sacrifice would not be necessary.
 * Hazama  also invokes Orochi imagery; one of his attacks involve creating a swarm of snake heads behind him. To make things even odder
 * In Otogi: Myth of Demons, the Yamata no Orochi (or its equivalent) is the guardian of the tower that separates the afterlife and life. Raikoh must climb the tower while avoiding the creature, as it is almost impossible to kill without the Moonlight Sword. If one has the sword, though, they can kill the Orochi in about one hit, and the prize for doing so is the Orchid Malevolence, a sword that kills everything in one hit, but also makes Raikoh a One Hit Point Wonder.
 * The Pokémon Hydreigon is partially based on one.
 * In Asuras Wrath  True form is a eight headed Orochi made of rock and lava, and is probably the biggest depiction of an Orochi ever.
 * In Asuras Wrath  True form is a eight headed Orochi made of rock and lava, and is probably the biggest depiction of an Orochi ever.