Re: Zanshin development
There is a training technique in expanding awareness that I have been taught and practiced. It goes like this.
Uketachi stands square with a shinai or bokken in gedan (low position to front).
Two Uchitachi stand on either side with shinai or bokken (preferably shinai) held in jodan (high overhead).
Uketachi holds his focus directly to the front at all times, preferably facing a wall some distance away. Uketachi tells both Uchitachi to shift back until uketachi can see that they are there, but cannot see the swords raised over their heads.
Then uchitachi each exchange glances to allow one or the other to strike the chest (mune) of uchitachi with big, wide horizontal cuts. (shinai, I said, or lightly with bokken)
Start slow. Uketachi turns hips strongly to the side of the strike raising to seigan (extended middle position), and then turns hips slightly inside the cut to receive and block it. Then return to front position gedan. Strikes should be random, and uchitachi should not try to hide or feint the cut at all. Cuts can be shortened and speeded up as Uketachi progresses.
Alternatively, if Ukeitachi is not yet prepared or is uncomfortable to block or sweep inside of a strike, then a tenkan on the foot away from the attacker can take them outside the arc of the cut in time with the strike. Get uketachi comfortable with this and then have uketachi begin blocking or sweeping inside with a pivot on both feet in place.
Once this method is learned then you graduate uketachi to receive yokomenuchi with an inside turning block, and then shomenuchi, with a rising vertical sweep (murabashi).