Normally, the various secret moves would stop if their forms were
broken. However, only in the situation that it were to return on the
proper trajectory of its slash, could it be held on for much longer.
Having noticed that in the duel between Kirito and Uolo, Liena-senpai
mastered it in a mere half month. The second hit of the
Serlut-style secret move, Whirling Current.

Kirito was Liena-senpai's valet, but as she graduated right after the
official match, he should not have had the time to learn this skill
directly from her. In other words, Kirito must have made his
master's skill his own after seeing it once as well.

This truly was how the relationship between the swordsman-intraining
and the valet trainee should be.

And this truly was the essence behind the sword.

(Alicization Turning, 166)