- "I will serve the Tokugawa as my father did, but in my own way."
- ―Hattori Masanari.[src]
Like his father, Masanari was a gifted warrior, and after Hanzō's death in 1596, Masanari succeeded his father as a retainer of the Tokugawa. His lethal skills in battle eventually saw him appointed the Captain of the Edo Castle guard.
However, Masanari was not as capable a leader as he was a warrior, and this led to him losing his position as Captain. Determined to salvage his reputation and that of the Hattori clan, Masanari fought valiantly at the Siege of Osaka in 1615, but did not survive.