Ronin Island (Ronin Island #1)

After a mysterious attack wipes out the major cities of 19th century Japan, Korea, and China, survivors from all three lands find refuge on a hidden island and build a new society.

Hana, the orphaned daughter of Korean peasants, and Kenichi, son of a great samurai leader, have little in common except for a mutual disdain for the other. But these young warriors will have to work together when an army invades the island with shocking news: there is a new Shogun and the Island is expected to pay fealty in exchange for protection from a new enemy... a mutated horde that threatens to wipe out all humanity.