I really like the back story, the legend of the blades, however, I agree with Chaosmark, knowing more about the blades, their power, appearance and their temptations would be really interesting, and if the quality of the writeup on the blades is the same as the backstory, you'll be in HoH territory.
Consider approaching a Strolenite whose work you like and propose a collaboration, if you're drying up on ideas/motivation for the blades.
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An idea for a plot or subplot is to have a religious order train or seek people that have the qualities of the 7 virtues to be the bearers of these blades. Such as a person with extreme amounts of personal temperance wields the gluttony blade... or someone that has practiced chastity for decades is given the lust blade.
The character conflict could be amazing
This is so unique and hillarious that the short description provided is truly sufficient.
I'd add but two things:
*Traceability of the coin: can mediums or the like trace where a coin has been?
*Interception of the coin: I echo a previous comment: could a thieving Potter clone snatch them from mid-air to enrich himself? Sure, their enchantment needs to be temporarily suppressed, but perhaps... perhaps catching them is something only a few extremely dextrous individuals could do, making Falcon Coin theft a way of living for a few, while ensuing most transfers are safe.