Hattori Hanzo began his training from a very young age, and some say he began learning the sword as early as the age of eight. Hanzo, in some Japanese stories, climbed a mountain as a child and met ancient teachers of the sword and mystics.

Hattori Hanzō rendered meritorious service during the Battle of Mikatagahara and became commander of an Iga Unit consisting of 150 men. During Mikatagahara, he captured a Takeda spy named Chikuan and when Takeda's troops invaded Totomi, Hanzō counter-attacked with only 30 men at the Tenryū River.

Hanzo, in a Japanese legend, served Tokugawa in an attack at night on Kaminogo castle in 1562 and was successful in retrieving the daughters of Tokugawa who had been captured by a rival clan. Hattori Hanzo would have been just sixteen years old at this point, but he had already caught the attention of Tokugawa Ieyasu who praised him for his bravery.

The rescue of Tokugawa’s daughters is the first glimpse of Hanzo’s supposed ninja life as opposed to his more honorable samurai way of living. Hanzo, Japanese legend states, used guerrilla warfare when taking Kaminogo castle, sneaking up on enemies, surprising them with attacks from above, and infiltrating through the castle guards.

Impressed with Hanzo, Ieyasu began to employ more ninjas and assigned Hanzo as their leader. After this, Hattori Hanzo was no longer referred to as a traditional samurai and became something of a leader of ninjas — most of which were from the province of Iga where the Hattori family originated from.