S. M. Stirling

"Princess Orlaith, heir to Rudi Mackenzie, Artos the First, High King of Montival, now wields the Sword of the Lady--and faces a new enemy. Fortunately, she also has a new ally in Reiko, Empress of Japan, who has been pursued to America by a conquering army from Asia. To combat their mutual foe, Orlaith and Reiko embark on a quest to find the fabled Kusanagi-no-Tsurugi, the Grass-Cutting Sword, one of the three great treasures of the Japanese Imperial...