Forum:Citidel of Endymion vs. Any other field card

Magical citadel of Endymion is a field card that acts as a spell counter bank. One of it's effects is "If this card would be destroyed you can remove one spell counter from it instead. if it's already out on the field and your opponent activates their field card, normally mine would be destroyed but if i remove a spell counter from it what happens? this has happened a few times and i don't know the official outcome. help