When talking about the technique it is called “Migi No Harai Tsuki”. When issuing the command for the technique it is “Migi wo harae tsuke”.
Terada sensei performs the kihon (basic) version of the technique at 00:26. Reach forward with the mokuju and rapidly bring it back into kamae knocking the opponents mokuju off the centre line then tsuki the opening created immediately.
As with most techniques the basic version is larger than the shiai version to emphasise the fundamentals of the technique. For harai the key fundamentals are that:
The strike to the opponents mokuju uses the “blade” of your mokuju. Striking with the side of the barrel will invariably result in your mokuju sliding away from your target area and have less impact on the opponents kamae. At 00:45 the angle of Terada sensei’s mokuju while reaching forwards is clear. This angle makes striking with the blade easier. A good strike with the blade will sound different to a strike with the side of the barrel.
The movement stops as close to immediately after striking the mokuju as possible. If your mokuju goes past the centre line you are giving your opponent an opening. Especially if they are able to avoid your harai. Ideally you complete the harai downwards motion in kamae. At 00:24 you can see Lukasz achieve this and at 00:27 not quite achieve it.
The initial movement of the harai is forwards and up. Do not bend the front elbow and lift your mokuju tip straight up. Instead reach forward and slightly above the opponnents rear shoulder. Lifting straight up will probably result in a weak harai using the front hand to “push” through the centre line. This will often result in your front hand being tensed and you will find performing a fast and accurate strike difficult. Using the front hand will also often mean you have less distance to work with for the tsuki.
At 01:00 you can see the exercise I do to try and get this movement into muscle memory. In this exercise keep the front arm in the same shape during the whole exercise and focus on pushing and pulling with the rear hand. At 01:22 you can see that by bringing the rear hand out from the body instead of forwards and bending the front elbow even a little creates an opening in Klara’s attack.
The strike to the opponents mokuju is as close to their front hand as possible. Knocking the tip of their mokuju away will probably not give you a useable opening, striking near the hand will more likely result in an opening the opponent cannot recover quickly from.
Kiai has been taught to us in two different ways in one version you kiai once with the harai and again with the tsuki. The first kiai is shorter and I think is to aid in making your harai a sharp and definitive blow to the opponents mokuju. The second way is to only kiai with the tsuki, I believe this is because the tsuki is after all the important bit.
Footwork for the strike I have seen several versions each with advantages.
A single step: This is probably the hardest to do smoothly. The aim seems to be to complete the harai and tsuki in the time of a single normal step. Obviously this, if done correctly, is going to be the fastest. However due to the distance also being the shortest you are probably in range for the opponent during the harai and so any flaw in your technique may give the opponent a chance to score.
One and a half steps: This is my favourite. As you are reaching forward for the first half of the harai movement bring your back foot up to touch your front foot. Then do the downwards part of the harai and the tsuki during the single step forward. I like this as it allows you to cover more distance and so there is less change your opponent can take advantage of openings. Bringing the back foot up like this can be very useful so long as you maintain correct posture and kamae as you have effectively taken a half step forward while appearing to still be at the same distance.
Two steps: Perform the harai with one step forwards and then the tsuki with another step. This is often the easiest to learn at the beginning. That doesn’t make it ineffective though. The step with the harai allows much more power to be directed into the opponents mokuju. I tend to make the first step very small (otherwise I am too close to tsuki) and often this results in the opponent opening Ura as resisting the extra power can cause the opponent to overcorrect while moving back to kamae.
For kihon Harai we commonly do three stikes similar to chokutotsu san bon and To-Ma as shown at the begining of the video. To-Ma we usually do two strikes with the motodachi creating the distance between each strike.
Receive the same as when receiving Omote. Especially when the student is first learning try to have a consistent amount of resistance to the harai for the series of strikes allowing the student to work on the technique without having to adjust for different strengths of resistance. Do not move the mokuju off centre yourself, ensure that the student strikes and creates the opening.