It's not about the "47 Ronin". It's quite a good read and will be an excellent movie some day.

From Publishers Weekly:
Bob Lee Swagger, retired marine master sniper and hero of bestseller Hunter's 1993 thriller, Point of Impact (forthcoming as the film Shooter), returns in this riveting homage to the myth of the samurai. Philip Yano, the son of the Japanese officer who commanded the bunker on Iwo Jima where Swagger's marine father won the Medal of Honor in 1945, approaches Swagger about a missing sword wielded by his father, Hideki, during the battle for the island. The sword turns out to be not just a family heirloom but a national treasure that evokes echoes from the most sacrosanct corners of Japanese history. Yano's search reveals there are those who will gladly kill for the honor it bestows upon the possessor. Plunged into a Japan where honor and loyalty outweigh even one's own life, Swagger finds that an old warrior like himself still has much to understand. While the action builds to the inevitable climax, the joy of the journey will keep readers turning the pages.

Here's the link to amazon.com