According to the description in the game for the Enduring Brooch, it's:
A brooch that will prevent you from going down once per battle.
But what exactly does it mean by "going down?"
Does that apply to the character that has it equipped and prevents them from being knocked out? Does that mean the if everyone is knocked out, they come back?
I had it equipped through some tough battles and the character that had it equipped still got knocked out like normal, and I still lost the battle when everyone was knocked out.