A moment ago.
Nathan released his bullets into the sky for the second time.
Knowing Nathan's way of utilizing the bullets, the worm focused on the three bullets that came toward Sera's familiars. He put special attention toward Brunhild, considering she was the only one who had enough damage to hurt him.
That was why the moment it sensed the movement of the bullet around Brunhild, it immediately leaped toward her, trying to sabotage her movement.
Brunhild was confused because the bullet didn't change its direction. It simply hit the worm and left no damage.
She did land another hit on the worm, but because the worm threw all his momentum and weight, it was impossible to fight it head-on.
As a result, she was getting pushed back until the worm started falling to the ground.
Bam!