Sekiro: Shadows Die Twice big shield enemy guide
To kill the big shield guys in Sekiro: Shadows Die Twice simply don't lock onto them. If you are not locked onto this enemy, you can just walk around them faster than they can turn, and then swing into their back. Repeat this process until they are dead.
This enemy can also be killed with the shinobi axe prosthetic tool upgrade, which breaks their shield. The axe is faster, but the cheesy way of killing it is more entertaining.
Below is a Sekiro guide video detailing how to do this simple trick and defeat this basic foe.
That's all there is to it, beating this enemy is as simple as that.