That's Kirigakure Saizoo. Who is Kirigakure Saizoo? Well, he was a folkloric shinobi, or ninja, who may, or may not have actually existed in feudal Japan. In myth, he was one of ten super-ninjas who worked for a warlord named Yukimura Sanada. This group is known as the "Ten Heroes", or "Ten Braves". Sasuke Sarutobi, the protagonist of "Samurai Spy", is likewise a folkloric figure, who also may or may not have actually lived, and who, ostensibly, was also numbered among Sanada's "Ten Heroes". Thus it can be assumed that Kirigakure Saizoo arrives in the nick of time to aid his comrade in arms. Kind of like if in the final frames of a Batman movie, Superman showed up to beat the Joker because both heroes are members of the Justice League.
