Immediately before the big Monster Association battle, the Class-S heroes hold a strategy meeting. Unfortunately, they just aren't in sync, and when Sweet Mask barges in, the situation only gets worse. Thankfully, King appears just in time to boost their morale and it's a good thing, too, because the big monster battle begins!
Volume 21 features extended front and back covers.
- Buyers of the Volume will have a chance to win a T-Shirt with the Volumes 19-21 cover spreads printed on it, with a total of 500 winners.