I used to do Shotokan Karate. When blocking, they taught me to wait for the last possible moment and then block. You do this so your opponent can’t react and change their attack. The block is meant to be both defense and a counter. Knocking away the incoming punch/kick, and ideally doing some damage as well. Toshio and Natsuno have waited and waited. Watching the town being withered away. Watching their friends, family and even themselves die out. But finally in the 18th episode, they counter. And oh, what a counter.