After the seven-year timeskip, Clare (the Organization's former No. 47), in memory of Flora, was shown to have mastered the technique, using it effectively and technical effortlessness during her battle with Agatha.
The Windcutter is a lightning-fast slashing attack, similar to the Quicksword, that involves drawing, swinging, and resheathing the sword in the blink of an eye. It is shown to be very accurate and fundamentally does not require any yoki to execute; however, the user can augment the speed and power of the technique by releasing yoki if she so wishes.
After the Northern Campaign, the Seven Ghosts were forced to suppress their yoki auras. Since the Quicksword uses yoki, Clare was forced to seal away the technique or risk leaking yoki into the world. As a solution, as well as in honor of her former captain, Clare began to use the Windcutter and eventually mastered it.
Comparison between the Windcutter and the QuickswordEdit
After the first skirmish in Pieta, Flora challenged Clare to a quick duel in order to test her Windcutter against the latter's Quicksword. It was determined that Flora's Windcutter was slower, but had more precision and strength than Clare's Quicksword. At the time of the battle with Clare, it is shown that the full power of the windcutter is equal to that of Clare's quicksword (however Clare's quicksword improves and surpasses Flora's windcutter technique). After the confrontation, Flora surrendered the title of "Fastest Sword Among The Claymores" to Clare.
Although the Windcutter is slower than the Quicksword, its accuracy is superior, thus making the techniques comparable in combat power. The Windcutter's use of intrinsic arm strength in favor of bursts of yoki also allows it to be used by warriors who have their yoki suppressed.
While both techniques are similar in nature, they are fundamentally opposite. The Quicksword is based solely on yoki, requiring that the user release a very large amount of yoki into one arm, essentially resulting in a partial Awakening; in comparison, the Windcutter utilizes base physical strength and speed. As such, it seems that users of the Quicksword cannot easily master the Windcutter if they lack the natural agility and arm strength to do so. The reverse, therefore, would also be true: without strong willpower, a user of the Windcutter could not control the release of yoki required to perform the Quicksword. This is demonstrated in the fact that Clare required many years of honing her basic arm speed to become capable of using the Windcutter, despite having mastered the Quicksword.