Here are some articles about Ripple tech @ Japanese banks:
https://ripple.com/insights/forty-seven-japanese-banks-move-towards-commercial-phase-using-ripple/
https://www.cryptocoinsnews.com/japan-banks-blockchain-digital-currencies/

So for now, the Pilot program is using Ripple, however on second url they state:

Aside from using Ripple, the banking group is also considering the possibility of creating a new virtual currency used exclusively by the participating financial institutions for the test. Details of any other digital currencies under consideration are currently scarce.