It is the Sengoku period, a time when Japan's states are constantly at war.  When the parents of Kasumi and her little brother are killed, they're adopted by a powerful warlord. Soon she joins the Kuniochi (lady ninja) to protect her brother and defend her new people. When one of their spies turns up dead, Kasumi must investigate. She eventually discovers that their spy was killed by a rival clan of swordmasters. Kasumi doles out the revenge but is injured in the process, and is looked after by a charming young man, Shingo. She must now choose between love and the code of the Kunoichi.