A method for managing fractional reserves of blockchain currency includes: storing, in a first central account, a fiat amount associated with a fiat currency; storing, in a second central account, a blockchain amount associated with a blockchain currency; storing a plurality of account profiles, each profile including a fiat currency amount, blockchain currency amount, account identifier, and address; receiving a transaction message associated with a payment transaction, the message being formatted based on one or more standards and including a plurality of data elements, including a data element reserved for private use including a specific address and a transaction amount; identifying a specific account profile that includes the specific address included in the data element in the received transaction message; and updating the blockchain currency amount included in the identified specific account profile based on the transaction amount included in the data element in the received transaction message.