In the beginning, BTC could be used to exchange of low value of virtual items, such as buying web sites or game points, virtual items, etc., afterwards, some people in order to get these virtual items, items may be in online auction own reality for BTC, others want to buy the real goods, but no BTC at hand, and then use real money to exchange BTC, as a result, BTC begin to flow, and have a "value".
In other words, bitcoin is inherently valuable as a means of payment; If it loses its function as a means of payment, it becomes worthless.
The value of money: it exists because of payment.
I think Bitcoin is considerable as currency because Bitcoin is a flexible crypto which allow everybody to used it as medium of payment and transactions which a lot better than the usual and I think we can consider Bitcoij as currency in such that it acts like one , it has the fundamentals of currency that we have taraditionally like depreciation and fluctuation it just that in crypto it rapidly occur.