The time is late summer in the year 1580. The place is ancient Japan.
Nasty monsters are on the rampage.
In particular, these monsters are attacking the three original schools of martial arts, the Hyuga Ninjas, Kasumi Ninjas and Hagakure Ninjas. The first two schools have already fallen to the advances of the evil nasty monsters. Entrusted to Ayame, the last of the Kasumi Ninja, is an ancient short sword with a legend that says when it and its three other companion weapons are brought together they can defeat evil and bring peace. As fate would also have it, entrusted to Sakon the Whirlwind, last of the Hyuga Ninja is a long sword with a similar tale. And, as the plot is written, the last weapon, a halberd, is in the hands of Ryoma Kogure of the Hagakure Ninja.