You can equip weapons and shields midbattle.

Or maybe you can say "LOOK KEFKA BEHIND YOU!"

and he'll turn around and go "what!?"

and you throw the extra atma weapon at the back of his head

EDIT: Graedus is in the monster-in-a-box in the cave to the ancient castle. I believe it makes you fight a Master Pug?

However, betting it nets you a... Dirk. Sucks, huh?