I think this is the first time we have seen one of the kids transform into a Hiruko. So, they die from this disease(?) and then their body transforms it seems. That little bit that was left over after Tarao's cremation, is that like a seed that takes over the corpse? I wonder if cremation is actually enough to prevent the Hiruko from manifesting.
I love the way that spatial distortion is drawn. Such a brutal way to go, having half your body displaced away.