Chief Cuckoo, I Wish You Well
This target has the authentic Japanese name Chief Cuckoo. He is one of The Kabukimono Chain which is unlocked after Naoe speaks with Shin'nyo. You can dispatch scouts to locate him but I found him on my own. The clues were pretty good.
In order to assassinate Chief Cuckoo with one stroke of the Hidden Blade, you'll need to obtain "Improved Ground Assassinate: Naoe removes 1 additional Health Segments with Ground Assassinations" in Naoe's Assassin Skill Tree (or enable the "Guaranteed Assassination" option under "Difficulty Tuning").
Now the fun part: get in to Katano Oil Trading, assassinate Cuckoo, and escape without engaging any guards. Chief Cuckoo walks in a predictable path, usually with two henchmen right behind him. A well is one of his stops, so let's assassinate him from the hiding spot and drop his corpse down the well.
A brute usually guards the well. You can drop down when he's out on patrol or, as in this video, while his back is turned. Just be careful not to land close behind him or he will hear you. I used 
to descend rather than 
.
When Chief Cuckoo approaches you can identify him by holding 
to look. Sometimes he stands right in front of the well for an easy assassination. Other times he stands off to one side. Mash 
to assassinate him before he can make up his mind.
Assassinating Cuckoo exposes Naoe, so remaining in the well is not an option. For my escape, I chose to sprint out the main entrance, bumping into the bouncer on the way.