From the Muromachi period (1336-1573) to the Edo period (1603-1868), Ninja were employed by warring feudal lords in various regions.
The Ninja's missions included night raids, sabotage, and assassination, but the most important mission was to invade the enemy's camp, gather information on the enemy's situation, and convey this information to the lord.
Thus, because the Ninja needed to survive and return to their lord living in castles, they often used weapons to protect themselves, such as Swords, Shurikens, Makibishi etc.