In Japan, interest rates are set by the Bank of Japan's Policy Board in its Monetary Policy Meetings. The BoJ's official interest rate is the discount rate. Monetary Policy Meetings produce a guideline for money market operations in inter-meeting periods and this guideline is written in terms of a target for the uncollateralized overnight call rate.
A higher than expected figure should be seen as positive (bullish) for the JPY while a lower than expected figure should be seen as negative (bearish) for the JPY.