The Fatal And Funny Weakness
William knew he had to bypass the direction these pieces were travelling through. And that meant he had to select one of the two directions available for him.
Either he'd go around the route of these pieces from outside or move closer to the array. And he indeed selected the latter.
He and Ibra came from that direction, clearing many monsters on their path. But when William went there, he was surprised to see lots of monsters lurking there, and many were running after the flying pieces as dogs trying to catch thrown balls or something.
If he used his sword, he'd move slowly and would take longer to kill these monsters and clear a path for him. He could have used his lightning technique, but that would exhaust his spirit power faster than he wanted.
So, the only option he got was his knives, and his bow and arrows!
He didn't use these arrows lately as he depended more on his sword and knives. But as his sword was out of the picture, he decided to switch it for his bow and arrows.