I do not own Inuyasha; it is owned by Rumiko Takahashi.
Mythology
In the beginning the Earth’s eldest children had sole dominion over the Land. They were a gift to his first bride, the Sun. She named them Youkai, the demons, and gave them gifts of her own. They were long-lived compared to most other animals inhabiting the Land, having life spans like the tallest trees and sometimes even the rocks on the Land itself. And though the Sun allied them with certain animals—dogs, cats, birds for example—Youkai were different from their counterparts. They had speed and strength, cunning and intelligence, beauty and dignity. From the moment they appeared on the Land they had unquestioned authority and quickly organized into societies, made up of families, loyalties, and rankings. The Youkai ruled the Land and, but for an occasional territorial dispute, through a system of alliances and treaties, the Youkai Era was peaceful.
After a time the Earth decided to take a second wife. He wanted a companion during the night as well as the day, and though her strength waxed and waned every month, the cool, aloof beauty of the Moon balanced the hot, fierce beauty of the Sun. The gift given to the Moon was the Earth’s youngest children, Ningen, the humans. At first Ningen were like Youkai, matched in all ways. But the Sun protested. She believed as first wife her gift should surpass that of the second wife. So the Earth diminished the Ningen in many ways. They became slower, weaker, plainer, and more short-lived compared to Youkai.
Then the Moon complained that Ningen would end up slaves to Youkai and they needed protection. After wondering what possessed him to take a second wife, never mind any wives at all, the Earth promised that human reproduction would be sped up—that a human woman could give birth once a year if desired, ensuring they would always be numerous. He also created the institution of the miko, priestesses skilled in weapons, magic, and healing who would protect and defend humans from Youkai that may wish them harm. So what passed as balance was established, and there was harmony in the household of the Earth.
Reality
On the Land, Youkai and Ningen coexisted, but with much distrust and unease. Ningen were seen by Youkai as distinctly inferior, and Youkai in turn were considered oppressors. Tensions increased over the years as Ningen populations expanded quickly. Their need for land and natural resources grew as their numbers swelled. Youkai saw this as a threat that required immediate eradication. A great army was assembled with the intent of the slaughter of as many Ningen as possible and the enslavement of the survivors.
However their belief that humans were little better than animals blinded the Youkai, and they were shocked and unprepared for the force that met their army. It was huge, well trained, and bravely willing to fight to the death. The humans were armed with weapons that were almost on par with those wielded by many demons. Their leaders had knowledge of battle tactics. But the most surprising element was the group of miko. They excelled at bow and sword, adept at long range and short range attack and defense. They could erect energy barriers for protection and could use energy as a weapon, killing lesser Youkai with ease. The First Battle of The War With No End continued for three days, heavy loss of life experienced by both sides. As the two camps retreated from the bloody plain, no victor apparent, one thing was clear—this was far from finished.
For generations the fighting continued intermittently, both sides at times playing aggressor, some years bloodier than others. Occasionally those tired of war and violence prevailed and an effort at treaty was attempted, sometimes resulting in years of stability. But inevitably the uneasy peace was always broken, and the only real accomplishment was the rage and hatred Youkai and Ningen societies felt toward each other increased with each generation.
Present
It is the year 1765 of the Warring Era. After a decade-long stretch of near-constant bloodshed, both sides in The War With No End are at a breaking point. The prominent families have received devastating losses. Pillage and destruction have rendered many settlements nearly uninhabitable. Displaced masses bring overcrowding and disease to remaining settlements and famine looms on the horizon.
It is in this context that a diplomatic contingent of Youkai make contact with a group of Ningen generals who have become vocal critics of the current situation and hint at willingness to negotiate. The Youkai propose a new treaty, a shocking marital alliance with great personal risks for both sides. Success could mean War’s End and the beginning of a new era. Failure would continue the death and misery, and take the Earth’s eldest and youngest children one step closer to extinction of one or both of their species. It is here that our story begins.