This is Parts 4 and 5 of a seven-part English translation of an article by Nakamura Sensei, 7th Dan. Posted with permission from Nakamura sensei and translated by KendoNotes.
I shall add to the explanation of seme.
With regards to the height of the ken-saki (sword tip) when the right foot slides forward during semekomi. I set it to the height of the chest and solar plexis, bring in my shinai below my opponent’s shinai and apply seme to the lower part of the opponent’s tsuba etc. The effectiveness of this varies with the opponent. Please check to make sure.
During the entire step of seme, please do not raise your hands.
As the right foot slides forward and is about to land on the floor, please fly in towards the men with a “tong” (sound effect). It may be difficult initially to not raise the hands as one extends the right leg. However, you can definitely do it. Next, my “extreme” seme. I relax my hands, shift my ken-saki away from the oponent’s men and seme-komi in. Of course, I offer “please hit my men.” In response, most people come into strike men. However, because my ken-saki is off-center, (my) men (strike) is late. In this case, I respond with a nuki-do or kaeshi-do.
For 7th Dan, you need to have the power to draw out the opponent (hikidasu). The recent passing rate for 7th Dan is 9%. It was about 22% six years earlier when I tested.
From seme to the stage of the strike, I shall write about the method of striking with tenouchi.
With regards to the part on seme, one strikes with “tong” (sound effect) when cues that the opponent will strike are detected. However, extend the left fist forward and strike as if nicking the nose of the opponent’s men (mengane).
Please be careful here not to pull and raise the right hand. If the left fist is pushed forward, the shinai will rotate about the shinai’s center of balance and the ken-saki will come up pointing upwards. Rather than only rising upwards, it will come fairly close to one’s body.
Once this point is reached, it will feel as if the opponent’s men is below your shinai.
From here, the right hand pushes the shinai and, while aiming for the opponent’s men, the ken-saki surges forward. The right hand is also referred to as the pushing hand (oshite). The job of the right hand is only to go hit the opponent’s men. However, the (job of the) extended left hand changes simultaneously to that of a pulling hand. Even though it may be called the pulling hand, the feeling is as if the left fist returns to the solar plexus area.
With the action of these two hands, the sword gains cutting power and one strikes a tremendously sharp men. After the strike, the body (using the hips) advances forward and assumes zanshin.
With regards to the position of the left fist when swinging, it is (raised to) at about the height of the mouth. According to the fundamentals, the left fist is raised up to the forehead. However, with a large swing, it would take about two heart beats to strike and one cannot really strike (this way).
If one watches slow-motion videos of high level senseis, it is raised only to about the mouth. Nevertheless, the ken-saki comes above one’s head. I think this way it looks as if the swing is large. In the case of the kiri-otoshi waza, the left fist is raised slightly higher.
If one commits to memory this operation of extending the left fist forward, one can use a heavy shinai. No matter how heavy it may be, as long as the left fist is pushed forward, the ken-saki comes up above the shinai’s center of balance. Afterwards, as mentioned a little earlier, it is just the operation of the right and left hands.
If this operation succeeds, it will lead to (comments such as) “the tenouchi is good” or “crisp strikes”.
 Translation note: I think 辺り instead of 当たり in「 水月当たりまで」was intended in the original article due to the context and the same kun-yomi.