Putting the two swords side by side, Nephis spoke:
"Your sword can be used with one hand, but its true potential can only be revealed when held in both. It is created primarily for cutting and severing, hence the higher center of gravity. However, it can thrust as well."
Then she gestured to hers:
"My sword is a bit more versatile. It is created for both cutting and thrusting, and it has a double edge. However, the principle of wielding these two swords is effectively is the same."
She took the sword in both hands, placing one near the guard and another near the pommel. Then, she performed a downward slash.
"They are both leverage-based weapons. When held with two hands, one hand pushes," she pushed the sword down with the hand near the guard. "While the other hand pulls."
The hand near the pommel simultaneously pulled the handle up, giving the blade a tremendous boost in speed.
"This is how you generate force and perform powerful strikes. Now, your turn."
Sunny looked at his sword and gripped it with both hands, mimicking Nephis's pose. Then, he raised it and slashed down, making sure to enhance the force of the strike with his lower hand.
Changing Star observed him.
"You need to understand that a strike doesn't come from the hands. It comes from your whole body. Power comes from your feet, your hips, your core, your shoulders, and is only then transmitted to your hands. Like this."
She demonstrated the downward slash again. This time, Sunny paid attention to the overall stance and movements of every part of Changing Star's body, as opposed to only the sword.
He wasn't a novice to fighting: instinctively, he already knew how to deliver a proper punch… even if, before, there wasn't a lot of strength in his body. The principles of striking with a sword were largely the same, so Sunny quickly understood the overall concept.
He performed the simple downward slash a few more times. After each time, Nephis gave him pointers and corrected his mistakes. Some time later, she was finally satisfied with his form.
"Good."
Sunny smiled, proud of his achievements.
Nephis looked at him thoughtfully and nodded.
"Now, do it a thousand more times."
The smile froze on Sunny's face.
'A… thousand? Did she say a thousand?!'
He blinked.
"Uh… sorry. How many times?"
Changing Star tilted her head and thought for some time.
"Well… we don't have much time today. So, yes. Only a thousand."
'Ha. Ha-ha. "Only" a thousand, eh?'
Sunny forced himself to sound polite.
"I see. Alright."
As Nephis walked back to sit with Cassie, he turned to the sea and raised his sword.
'One'.
The Azure Blade whistled as it cut the air. He raised it again.
'Two.'
Push and pull. This is how you generate force.
'Three.'
Strike with your whole body, not just your hands.
'Four.'
As Sunny raised his sword and slashed down, over and over again, only one thought eventually remained in his mind:
'Repetition, experience, clarity. Repetition…'
By the time he was done performing a thousand strikes, Cassie was finally ready to speak.