First time you play the game in question, always make sure those temporary characters get generic equipment that can be bought anywhere.
As you learn the game and its events "by heart", you could un-equip them right before they leave you.
I always do that, anyway.
FYI, un-equipping this Ether from Minh and selling it is very helpful during the early parts of the game, because it goes for 1250 Gil.