After Vaan was done with the witches' corpses, he erased them with fire. Then, he took out the bodies of the Assembly of Silent Night's members.
Fortunately, the cave he created was large enough to accommodate them all, with more room to spare.
He settled the bodies on the edges of the cave for the time being, then made a large hole in the center with Earth Manipulation, followed by transmuting the earthen surface into metallic substances.
This was to avoid the ground soaking up the blood once he drained the bodies.
Once the preparations were ready, Vaan picked up the first body of an A-ranker, beheaded it, then placed the headless body on the edge of the empty pool, letting the blood flow out of the neck and into the pool.
Vaan repeated the process with each body until the blood pool was surrounded by headless bodies and ran out of space. Then, he started stacking the remaining headless bodies on top of the existing ones.