The USD/JPY is indeed bouncing at the key 78.6% Fibonacci retracement level of wave X (pink). The main confirmation whether price could start a bearish swing is whether it can break below the support trend line (green).
The USD/JPY is probably building a wave X (pink) if price indeed breaks below the support (green) of the bullish channel. A bullish breakout however could see price move higher towards 112.75-113.
The USD/JPY could be building a wave 1-2 (blue) pattern if price indeed completed a wave X (pink) pattern but the bearish breakout remains key. Otherwise price is still in an uptrend channel and a bullish bounce could see price make a continuation higher.