The 4th year of the Keian Era, Edo Period.

Forty-eight years had passed since Ieyasu, the sovereign of Japan, opened the capital to the Tokugawa shogunate. The reign of the Tokugawa was passed down to the fourth Shogun, Ietsuna. The number of people living in Edo increased day by day, and the city seemed to be enjoying its prosperity. However, due to a succession of dissolutions and revocations by the feudal lords, the streets were filled with ronin, and the peaceful days of Edo seemed to be fading.

In Asakusa, a town in Edo, there was a young man named Miyamoto Iori. He was the adopted son and apprentice of the great swordsman Miyamoto Musashi. Iori chose not to serve under a lord, but rather spent his days training his swordsmanship. One day, he noticed an unfamiliar bruise on the back of his hand. Iori would soon find himself trapped in the midst of a horrific conflict, a battle of blood and trickery.

The battle over the "Waxing Moon" which could grant any and all wishes - the "Waxing Moon Ritual". The seven individuals seeking their wish, or Masters, are the bearers of the Ritual. The seven Heroic Spirits, or Servants, are summoned to this world by their Masters. The curtain rises on the battle between the seven Masters with their seven Servants.

“I suppose...you're the one who summoned me?”