Ninja Code of Honor
The Ninja came to be during the 11th Century at about the time the Samurai came to power. The Ninja decided that they did not wish their lives (and deaths) to be controlled by some all powerful warlord. The Ninja relocated their families to the mountain regions in Japan and set up a counter culture. Here, all the family members worked for the good of the Clan.
In order to protect their families the Ninja developed many skills. Expert fighters taught Martial Arts (Tai-jutsu), Great riders taught Horsemanship (Ba-jutsu), and the Learned taught Academic and Science skills (Ten-mon, Chi mon).
The Ninja also became experts in explosives (Kayku-justsu), as well as many weapons. In fact, of all the Martial arts Ninjutsu has the most diverse array of weapons.
The Ninja believed that learning was for everyone and not just the rich. Children were taught the same skills as adults. The Ninja were also great Philosophers (Kyojitsu Tenkan Ho).
Because of all these skills the Ninja became feared warriors and tacticians. The warlords who had even one Ninja in there employ were deemed to be powerful and dangerous.
The new civilization flourished and with it, a new class of wealthy, privileged families. These families fought with one another in attempts to make or destroy emperors. The need for spies, informants and now assassins grew as these families dueled for power. They were suspicious and jealous of one another and would resort to any means necessary to eliminate any possible threats. Therefore, the practitioners of nonuse were in great demand. With this, the ninja was born.
At this point you must understand the samurai to truly understand just why the ninja were so effective and in such demand. The samurai's life was to "live by the sword, die by the sword", with no fear of death at all. His sword was his whole life, his soul. With this he followed the warriors code of honor, the Bushido. The bushido was to be followed at all times. If a samurai were to stray from the code he would then commit seppuku, another term for hara-kiri. This was a ritual suicide where they would cut their stomach open with their smaller sword.