The opening sequence of this film is a shot by shot recreation of the 1960s era original.
Matsudaira Naritsugu was a real historical figure. He lived from 1811 to 1835. He was lord of the area called Akashi which is nowadays in the Kansai area of Japan.
The 13 assassins plan to attack Matsudaira Naritsugu while his journeying to Edo (the old name for Tokyo). In the Edo period the lords of Japan had to travel and stay in Edo. This was called Sankin-kotai, or official journey. The lords stayed to show their loyalty to the shogun and the system helped the shogun keep tabs on the lords.
The film is set in 1845.
Koji Yakusho and Gorô Inagaki also played opponents in University of Laughs (2004) ("University of Laughs").