Yamata no Orochi

Yamata no Orochi (ヤマタノオロチ, also 八岐大蛇, 八俣遠呂智 or 八俣遠呂知), or simply Orochi (大蛇), is a legendary eight-headed and eight-tailed Japanese dragon/serpent.
Yamata no Orochi legends are originally recorded in two ancient texts about Japanese mythology and history. The 712 AD Kojiki transcribes this dragon name as 八岐遠呂智 and the 720 AD Nihon Shoki writes it as 八岐大蛇. In both versions of the Orochi myth, the Shinto storm god Susanoo (or "Susa-no-O") is expelled from Heaven for tricking his sister Amaterasu, the sun goddess.
After expulsion from Heaven, Susanoo encounters two "Earthly Deities" (國神, kunitsukami) near the head of the Hi River (簸川), now called the Hii River (斐伊川), in Izumo Province. They are weeping because they were forced to give the Orochi one of their daughters every year for seven years, and now they must sacrifice their eighth, Kushi-inada-hime (櫛名田比売, "comb/wondrous rice-field princess"), who Susanoo transforms into a kushi (櫛, "comb") for safekeeping. The Kojiki tells the following version:
The Nihongi also describes Yamata no Orochi: "It had an eight-forked head and an eight-forked tail; its eyes were red, like the winter-cherry; and on its back firs and cypresses were growing. As it crawled it extended over a space of eight hills and eight valleys." The botanical names used to describe this Orochi are akakagachi or hoozuki (winter cherry or Japanese lantern, Physalis alkekengi), hikage (club moss, Lycopodiopsida), hinoki (Japanese cypress, Chamaecyparis obtusa), and sugi (Japanese cedar, Cryptomeria).
The legendary sword Kusanagi-no-Tsurugi, which came from the tail of Yamata no Orochi, along with the Yata no Kagami mirror and Yasakani no Magatama jewel, became the three sacred Imperial Regalia of Japan.
The Japanese name orochi (大蛇) derives from Old Japanese woröti with a regular o- from wo- "shift", but its etymology is enigmatic. Besides this ancient orochi reading, the kanji, 大蛇, are commonly pronounced daija, "big snake; large serpent".
Carr notes that Japanese scholars have proposed "more than a dozen" orochi < woröti etymologies, while Western linguists have suggested loanwords from Austronesian, Tungusic, and Indo-European languages. The most feasible native etymological proposals are Japanese o- from o (尾, "tail", which is where Susanoo discovered the sacred sword), ō (大, "big; great"), or oro (峰, "peak; summit"); and -chi, meaning "god; spirit", cognate with the mizuchi river-dragon. Benedict originally proposed woröti "large snake" was suffixed from Proto-Austro-Japanese *(w)oröt-i acquired from Austronesian *[q]uḷəj, "snake; worm"; which he later modified to *(u-)orot-i from *[q,ʔ]oḷəj. Miller criticized Benedict for overlooking Old Japanese "worö 'tail' + suffix -ti – as well as an obvious Tungus etymology, [Proto-Tungus] *xürgü-či, 'the tailed one'", and notes "this apparently well-traveled orochi has now turned up in the speculation of the [Indo-European] folklorists." Littleton's hypothesis involves the three-headed monster Trisiras or Viśvarūpa, which has a mythological parallel because Indra killed it after giving it soma, wine, and food, but lacks a phonological connection.
Polycephalic or multi-headed animals are rare in biology, but commonly feature in mythology and heraldry. Multi-headed dragons, like the eight-headed Yamata no Orochi and three-headed Trisiras above, are a common motif in comparative mythology. For instance, multi-headed dragons in Greek mythology include the 9-headed Lernaean Hydra and the 100-headed Ladon, both slain by Heracles.
Two other Japanese examples derive from Buddhist importations of Indian dragon myths. Benzaiten, the Japanese form of Saraswati, supposedly killed a five-headed dragon at Enoshima in 552. Kuzuryū (九頭龍, "nine-headed dragon"), deriving from the nagarajas (snake-kings) Vasuki and Shesha, is worshipped at Togakushi Shrine in Nagano Prefecture. Compare the Nine-headed Bird (九頭鳥) in Chinese mythology.
Comparing folklore about polycephalic dragons and serpents, eight-headed creatures are less common than seven- or nine-headed ones. Among Japanese numerals, ya or hachi (八) can mean "many; varied" (e.g., yaoya (八百屋, lit. '800 store'), "greengrocer; jack-of-all-trades"). De Visser says the number 8 is "stereotypical" in legends about kings or gods riding dragons or having their carriages drawn by them. The slaying of the dragon is said to be similar to the legends of Cambodia, India, Persia, Western Asia, East Africa and the Mediterranean area. Smith identifies the mythic seven- or eight-headed dragons with the seven-spiked Pteria shell or eight-tentacled octopus.
The myth of a storm god fighting a sea serpent is itself a popular mythic trope potentially originating with the Proto-Indo-European religion and later transmitted into the religions of the ancient Near East most likely initially through interaction with Hittite speaking peoples into Syria and the Fertile Crescent. This motif, known as chaoskampf (German for "struggle against chaos"), represents the clash between order and chaos. Often as these myths evolve from their source, the role of the storm god (often the head of a pantheon) is adopted by culture heroes or a personage symbolizing royalty. In many examples, the serpent god is often seen as multi-headed or multi-tailed.
The fight of a hero, sometimes of extraordinary birth, against a dragon who demands the sacrifice of maidens or princesses is a widespread tale. In folklore studies, it falls under the Aarne–Thompson–Uther Index ATU 300, "The Dragonslayer".