Why try and make the set so large?
If you have a few very nice, themed keys, the set price goes down compared to a lot of keys, where most of them aren't that closely themed anyway?
More people would be likely to pick up a $5-15 novelty set that is closely tied to firefly, rather than a $28 set with a bunch of keys that aren't quite so clearly themed.
If you reduce the options, people are either in the one pot, or not at all - decide to either be colour or black and white etc? something better than nothing?
Just some ideas I have seen thrown around for other sets that didn't reach MOQ.
Oh, did you go with just the kanji because of copyright on the circle in a circle firefly logo?