Grasscutter was the most epic storyline in the Usagi Yojimbo Comic book yet. It covered Dark Horse issues 13-22, with hints and events leading up to it in other issues as well. The writing of this epic, complete with all necessary historical research took creator Stan Sakai five years. The Sequel, Grasscutter II, ran from issue 39-45.
The story revolves around the mystical sword of japanese legends, the Kusanagi no Tsurugi, or Grasscutter. The sword, which could be called the Excalibur of Japan and which was lost at sea long ago, is found again and to be used in a conspiracy to topple the Shogunate and reinstate the power of the Emperor. But when the sword mistakenly ends up in Usagi's hands, the hunt is on. Add to that the involvement of the mysterious demon Jei and the Neko Ninja, as well as a plot to kill Lord Noriyuki, as friend of Usagi's and Tomoe's, and you have a truely grand story which I will not spoil by telling to much. The sequel, Grasscutter II deals with the quest to bring the sword to the Atsuta shrine in order to hide it and prevent it from being used for evil. But Usagi and his friends are chased by various ninja clans each with their own agenda.
As I mentioned above, the whole story is based on the legend of the Kusanagi no Tsurugi, or grass-cutting sword, one of the three holy heirlooms of the japanese royal family (the other two being a jewel and a mirror). They are said to have been presented to the royal family by the sun goddess Amaterasu herself. The Grasscutter was found in one of the tails of an eight-tailed snake. Originally, the sword was named Ame no Murakumo no Tsurigi (Sword of the Billowing clouds), and was kept in the Imperial Palace until the reign of the 10th Emperor, Sujin, who built the Kasanui shrine, installing his own daughter as priestess in care of two of Amaterasu's Treasures, The Mirror and The Sword. The shrine was later moved to Ise.
When prince Yamato-dake went out to subdue the Ebisu over one hundred fifteen years later, he received the sword from his aunt tohelp him in his quest. When he was trapped by the Ebisu within a wall of fire in tall grass, he used the sword to cut an insulating swath in the field, saving his life. Because of this event, the sword was renamed Kusanagi no Tsurugi.
Emperor Sujin also had copies of The Mirror and The Sword made that would host the spirits contained within the originals while the originals were used by the Emperor. Grasscutter and its spirit were installed at the great Atsuta Shrine in Owari. The original sword was lost at sea at the Battle of Dan no Ura, the final battle of the Heike Wars in 1168 A.D. (late Heian Era), and returned of the Dragon King of the sea. Or was it?
Depending on whose side you believe in, either the original or the copy was lost at sea in that battle. The losing Taira clan claimed the original sword went down, while the winning side, the Minamoto clan said that only the copy was lost. In Grasscutter, Sakai reconciled both positions by returning the original sword to Atsuta.