The Bo is a wooden staff of approximately 6ft., with which the ordinary man and travelling monk in feudal Japan wandered about. Only samurai were allowed to carry arms, and ordinary civilians had no choice but to use a seamlessly harmless weapon, and think of simple staff techniques, to fight off the sometimes bloodthirsty samurai.
In all its simplicity the Bo is a very effective weapon, contrary to the sword the Bo has two sides which can both be used to strike or stab an opponent. A well aimed blow with the Bo can break a sword or wound an enemy seriously.
Many samurai learned this the hard way and paid the ultimate price finding out.
Bo jutsu of Tenshinsho-den Katori Shinto Ryu consists of 6 kata for beginners (Omote no bo), and the opponent is armed with a ken. Just as in the 4 kata of Ken jutsu the students learn how to strike with the Bo and react to the opponents movements. The student-sword fighter learns how to fight against a weapon approximately twice the size of his own sword.
After several years of training with the bo, and after students have gained sufficient control in handling the bo, an additional 6 advanced kata can be taught (Gokui-no-Bo). These kata will teach students to fight bo versus bo, and thereby teach students to fight weapons of equal length.