"Let us stop him for you," yet before he'd even let his two monstrous weapons come closer, Sloth shouted, "Do whatever you need, and we'll buy you time."
"Thanks…" William knew that Sloth and other old masters got what he planned to do. Despite knowing how suicidal it was, they never tried to stop him. Instead, they chose to step up and stop that monster, not wasting the technique his two monstrous weapons were going to release.
Despite knowing how suicidal it was for them to do this, as they wouldn't have enough time to retreat from the surge of decaying spirit power, he never tried to stop them.
This wasn't a kindergarten, this was the spirit world. And in this world, living was an everyday challenge for any master!
He selected to do it, and they chose willingly to do their part. As the two sides understood each other's thoughts and feelings, they both went to execute their role with everything they had.