Sado didn't understand what Kenshin saw, he believed his sword strike to be dull, telegraphed and with poor form from what he had seen from various other skilled individuals. A problem he had was he was seeing everything as he would a taijutsu fight. He also picked apart his stance, and his ability comparing it to master swordsman and samurai.
His fighting style relied heavily on intercepting and counter-attacking with strong precise blows and with his training in medical ninjutsu this even more influenced his style as it allowed him to pick apart an opponent but he couldn't figure out how to transition that to this new style he was unfamiliar with.
He hadn't yet realized the potential a blade had for this that was until Kenshin drew his sword.
Sado watched Kenshin closely, noticing his form, he watched the sword unsheathe. Without thinking he cleared his mind of all thoughts exhaling a long somber breath as Kenshin began his offensive action. His perception of time slowed immensely as he watched Kenshin grip the sword in his right hand. His grip was relaxed, far more relaxed than his own, Sado knew now that he held the sword too tightly with too much force. He mentally noted this and would correct it the next time he had a chance. As Kenshin approached the tree Sado watched his grip tighten he noted this subtle change and compared it to his usual style only tightening his fists upon impact then relaxing them in an instant when he was done. It made sense now, it was the basis of economy of motion. Sado was wasting strength, power and force for no reason.
The first strike was an upward-diagonal strike, Sado realized Kenshin was using his feet and his footwork to carry momentum upward along with the strike. The blade cut through the tree cleanly and quickly, so cleanly in fact that Sado found it hard to see the fault-line from the cut. Without pause, seemingly without thought Kenshin seemed to change his footing throwing his weight and stance from his left foot to his right in unison to this Sado watched him perform the horizontal strike. It mimicked the first in that it was precise, clean and quick. So quick that without his enhanced and specialized senses for combat Sado knew he wouldn't have been able to track it.
Then Kenshin stepped back slightly, using his left leg to pull his entire body back while performing a downward diagonal slice along a similar fault-line as the last finishing at the lower left of the tree itself. Sado took notice of the fact that during this entire onslaught Kenshin held the sword in his right hand, never using both hands as Sado had until this final strike. This all happened at an immense speed, one that would be hard for him to track had he not had significant training in taijutsu and trained his senses to be on par or in some cases better than taijutsu masters
Sado knew that damage had been done, but the bark of the tree and it's trunk didn't seem to react. That was until Kenshin began to re-shethe his blade. The loud 'tink' noise echoed as the sword now rested in the sheath while the tree seemingly exploded with all of the destructive force. If Sado had not seen the blade strikes and the subtle faults in the tree he would have had no idea how it was done. Sado paused momentarily before speaking.
I see, my problem was that I was seeing the blade as a tool. Nothing more than a hammer to strike nails with, from what I just saw I need to see it as an extension of my own body. I have to be able to factor it into my own movements, I hadn't thought of that. I just believed if I treated my body as I would with taijutsu the stance, the fluidity and the force would work like it naturally does. I'll make the corrections to my form, stance, and movements this time.
As he spoke his grip on the sword loosened as his stance did too he took on a relaxed posture again taking on the Bai Jong stance. His muscles became less tense as he realized he was going at this the wrong way. He cracked his neck lightly as he took three steps forward towards the tree. He held the sword low against his left side as one would with a sheathed sword. He then took a fourth step forward as he held the sword in his right hand with a relaxed grip.
He performed an upward-diagonal strike holding the hilt in his right hand the sword traveled from the bottom left of the tree to the top right as his grip tightened upon impact and not a second before.
The blade would slice completely through the tree but left little to no actual visible damage unlike his last strike which had buckled and splintered the wood. Without pause his grip relaxed again as he drove the sword downward through the air and then back up the base of tree in another upward-diagonal strike this time from the bottom right to the top left again only tightening his grip upon impact. This would save energy, and be more efficient and effective than his previous haphazard and rough strike. As he did this he shifted his weight to his left foot using the momentum built up from the previous strike to carry through and continue on increasing the potential of the strike. This created an X like strike at a rapid pace happening in a fraction of a second his arm moved in the blink of an eye as he used his speed and fluidity to drive the blade completely through the tree.
Finally he lifted his left hand gripping the sword with both hands and brought it directly down through the center of both previous strikes and the tree itself creating a strike that would split the tree in half. He used his upper body by fluidly lifting and lowering his shoulders, which caused his upper arms and forearms to move swiftly and precisely as he used his lower body to force all of his weight into and through the tree. This final motion mimicked an axe-strike, a motion one would use to chop wood. He turned his entire body and took a step toward Kenshin as the tree popped apart it didn't explode as the tree did for Kenshin, but instead just made an audible 'pop' noise and fell to the ground becoming a pile of quarter-section tree pieces like a stack of firewood. It was about knee height.
Sado stood waiting still gripping the sword, with a relaxed posture as he took all of the knowledge he had obtained through years of taijutsu training and applied them to this new fighting style. He seemed to be a bit more confident with it now that he had grasped the basic concepts but knew he still had much more to learn.
Better?