This Achievement can be obtained on the sixth level of the game "
Hida Village".
In the final part of the level after you have eaves dropped onto one either one of the targets and regrouped with the rest of your team General Okkoto will spawn along side 1 samurai and 1 officer AI. The General is treated the same as a standard samurai unit so once you are in range shoot him to stun him then run up and finish him with melee this will cause the achievement to pop.