As he spoke, she decided to interrupt him with her movement. It was fine- He had said what he needed to say. She pushed off at him, causing him to delay only a fraction of a second. It was not due to her speed, but rather his own surprise that she had chosen to react in that manner. At the tournament she had been timid, trying to avoid front on confrontation. Now she seemed very trigger happy, choosing to jump on the opportunity to attack him rather than take the fight slowly. Where she had made a mistake was assuming that his stance made him unready for combat.
They say that at a certain level, one learned to feint weakness to draw in an enemy. That wasn't necessarily how Finn was doing it, but the idea was still the same. His loose grip on his sword that was as light as a broomstick served as a strength, not a detriment. It allowed him quick maneuverability both offensively and defensively that no one else could hope to match. So as she charged in, he chose to watch her close the distance. The only stance he had was a slight bending of one of his knees, but that had been that way while he was standing still. He made no obvious changes.
Finn had seen the blade that had been extended from her wrist, and its length. He knew, even if he'd be unable to see her, the timing it would take for her to reach withing striking range. As her foot stepped down at the four meter mark, he saw from the corner of his eye a blue something moving below her. He had to act in the moment, and currently he wished to test out his better mastery of his sword.
As she stepped on the ground, much faster than she herself could move, the blue slime below her spread out and rose. It was four meters in diameter with her at its epicenter, but Finn was four meters away from her. Due to that, it was much too short to reach him. However, with its speed, it did well to surround her and block out most of her vision, as it was too thick and full. Her blade, however, was piercing out at the same speed it had been going. With that, Finn could act appropriately.
Finn had cocked his elbow slightly as she had stepped at that four meter mark, the timing as such so that as she had reached that distance his elbow was already slightly bent. Twisting his left arm back as if to build momentum, he stabbed his sword forward and at an angle that it would collide with her blade as she recklessly charged forward at speeds that were roughly eight meters per second. As she came through her own attack, she'd have the time to see her swords pierced and destroyed as his sword would ram into her chest, through her own armor and piercing rather deep.
Her defensive spells that were cast prior, unbeknownst to him, were mere instant spells. They had long since left her body, as they would only last as long as they were fed mana. She did not have a full understanding of her own magic, and that had cost her this battle. As his sword pierced deeply through her chest, her own momentum had run her through it along with his stab. Twisting to the left now, Finn would grab her face with his left hand and rip his sword from her body. He stopped himself from slamming her to the ground, and instead tossed her backwards as if her body weighed nothing at all.
"I preferred the you I fought at the tournament." His words were cold, almost sad.