Black belts should wear the yoroi to understand the value of balance. When you are dressed with the yoroi, the weight is spread all around the body and not only on the back as we experienced it with a backpack.
Naturally the extra weight transforms the body repartition and we move with about 50% of our weight on each leg. This is why the kukishin ryû and the takagi yôshin ryû kamae do not have the same appearance compared to the togakure or other low kamae systems.
Peter on the picture is showing here the kosei no kamae as if he was receiving some kind of attack from his opponent. As though “kosei” means “attack” he is absorbing the blow with his protected forearm (aite to kumu kokoro gamae) and uses his legs to cushion it. Next he will spring forward and take uke‘s balance to counter-attack. Once the blow has been received, there is no power left in the weapon, the momentum is gone.
As sensei said back in 2003, concerning the yoroi kumiuchi: “when there are two attacks (body or weapon) they are not of the same quality”. The first attack is fuelled by the footwork and his strong and fast, the second starts where the first one was stopped and uses a different distance.
Note that the back hand stays at the hip level as if Peter was holding a tachi.
Every waza in Japan originated from yoroi kumiuchi.