Australia exports iron ore, coal and gas, largely to Asia, so the currency tends to rise when global industry is expanding and fall when it is not. That makes AUD/USD a rough sentiment barometer, often moving with equity indices rather than against them.
The Australian dollar has historically carried a higher policy rate than the yen or franc, which made it a favourite long leg in a carry-trade. When carry unwinds, AUD/JPY tends to fall hardest.
Example: a risk-off session sees the S&P 500 down 2%, AUD/USD down 0.9% from 0.6620 to 0.6560, and AUD/JPY down 1.8%. The cross falls further than either dollar pair because both legs move against the position.
Related: kiwi, carry-unwind, yen-cross