Shin would likely die if he received that blow directly, so as the greatsword approached from above his head, by putting his strength into his left foot, he bent himself backward and evaded it.
Rionne, who had just swung down her greatsword, couldn’t move right away because of the weight of her weapon.
From there, Shin did a horizontal kick, but Rionne crouched down and evaded it.
Shoom!
With her body twisted as she tripped, although she had just evaded Shin’s kick and stood only on one foot, she still didn’t stop attacking.