Bitcoin

Firstly, it does not appear to be a true "currency" but rather a payment system comparable to PayPal or similar systems (buyers and sellers of anonymous transactions don't really care about the value of bitcoins as they are simultaenously buying and selling them as by-product of a transaction)

Secondly, it is in precarious position as it is neither backed by a commodity nor (more importantly) can be utilized to satisfy a tax liability (in any fiat currency).

Thirdly, its has neither soft nor hard Power, so will be hunted down and killed by those who do.

Governments, like Orcs (or Dothraki or whatever fictional aggressive race you like), only respect Power.  If you don't have it, whatever you have of value will be confiscated or destroyed.