In the primordial age of the cosmos, the divine siblings born of the purification of Izanagi-no-Mikoto held sway over the realms of existence. Among them, Amaterasu-Omikami, the radiant goddess of the sun, ruled over Takamagahara, the High Celestial Plain. Her brother, Tsukuyomi-no-Mikoto, governed the silver shadows of the night. The youngest of the primary three siblings was Susanoo-no-Mikoto, a powerful deity of roaring winds, tempestuous storms, and the vast, unyielding seas. However, Susanoo was a god of turbulent emotions and untamed fury. He spent his days weeping and wailing, yearning for the sub-surface underworld of Ne-no-kuni, the domain of his deceased mother Izanami. His weeping was so ferocious that it dried up green mountains and caused oceans to boil with violent waves, disturbing the cosmic order.
His temper eventually escalated into open, reckless rebellion against his sister Amaterasu. When he ascended to Takamagahara to bid her farewell before departing for the underworld, Amaterasu suspected him of treasonous intent and met him clad in full warrior armor. To prove his peaceful intentions, they engaged in a ritual of pledge and creation, biting and chewing items of each other's clothing and ornaments to produce new deities. Yet, emboldened by the birth of male deities from his own sword, Susanoo grew boastful and wild. His subsequent actions shattered the peaceful peace of the heavenly fields. He destroyed the delicate ridges of the heavenly rice fields, filled up the irrigation ditches, and desecrated the sacred chambers. His most terrible act occurred within Amaterasu's sacred weaving hall, where he threw a flayed heavenly piebald stallion through the roof, causing such panic that one of the weaving maidens accidentally took her own life. Heartbroken and terrified by her brother's unhinged ferocity, Amaterasu fled into the Ama-no-Iwato, the Heavenly Rock Cave, plunging the entire universe into cold, terrifying darkness.
Though the assembly of eight million kami eventually devised a cunning plan of dance and laughter to lure Amaterasu out of her self-imposed exile, the peace of Heaven could not be restored until justice was served. The heavenly assembly held council to determine Susanoo's punishment. For his unprecedented crimes, they imposed upon him a vast tribute of compensatory gifts, shaved his beard, pulled out his fingernails and toenails to neutralize his destructive physical force, and formally banished him from the High Celestial Plain. Stripped of his divine home, his grand status, and his heavenly comforts, the disgraced storm god was cast down to the earthly realm of mortals, descending through the thick clouds to the province of Izumo.
Susanoo landed at the headwaters of the Hi River on a mountain known as Mount Sentsu, situated in what is modern-day Shimane Prefecture. Alone in this unfamiliar wilderness, the banished god walked along the banks of the rushing river, trying to orient himself in his new, humble life. As he wandered, he noticed chopsticks floating down the stream from a higher elevation. Realizing that there must be humans living upstream, he decided to investigate, hoping to find shelter or sustenance.
Following the river, Susanoo came upon an old man and an old woman weeping bitterly, with a beautiful young maiden seated between them, her tears falling into the soft earth. Susanoo approached the weeping trio and demanded to know their identities and the cause of their profound grief. The old man looked up at the wild-haired stranger and answered, 'I am an earthly deity named Ashinazuchi, a son of the mountain god Oyamatsumi. This is my wife, Tenazuchi, and this is our daughter, Kushinadahime.'
When Susanoo asked why they wept so pitifully, Ashinazuchi explained their tragic circumstance. 'We once had eight beautiful daughters,' the old man sobbed. 'But every year, a terrible, colossal monster known as the Yamata no Orochi—the eight-headed serpent of Koshi—comes to our valley to devour one of our children. Now, the time of its annual return has arrived, and Kushinadahime is our last remaining daughter. There is no escape, and we must give her up to the beast.'
Susanoo listened intently, his fierce nature instantly stirred by the prospect of fighting a legendary beast. He asked the old man to describe the monster. Ashinazuchi shuddered as he spoke: 'Its eyes are as red as winter cherries. It has a single body with eight heads and eight tails. Over its enormous back grow moss, cypress, and cedar trees. Its length is so immense that it spans eight valleys and eight hills, and its underbelly is perpetually inflamed, dripping with blood and slime.'