This is how to get Yashichi #6 in the docks (area 6).

This one sucks.
You need to make your way to the top of the first building, and make it to where the second droid soldier is.
Kill him and grapple onto the light pole from the purple containers, slide off and try to grapple to the next one over.
Do this again until you reach the next one, pull up and turn around and shoot left to the platform.
The Yashichi is up here.
If you fall while trying, it's not easy to get back up...