You could try pulling the fabric along the bias to stretch it and see if it makes the letters crack enough to pick off. I highly doubt it'll work, though. And even if it does, it'll take forever to pick all that crap off.
(And hopefully the pulling doesn't damage the fabric, either. Those bagged costumes are usually made from really crappy material.)
You'll probably either have to paint over it or put an applique over it.
FF9 cosplay? Hit me up!
2014: Anime Los Angeles, Anime Conji, and whatever else falls into my lap
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