JPY is quite unique to many traders, especially to a forex trader because it is seen as a barometer for risk. Many traders use it to gauge whether the market is currently risk-on or risk-off.
Risk-on references when the market is bullish; the Yen is weaker against the USD during this time. Risk-off refers to the direct opposite. Note, when bad news occurs in Japan, the Yen strengths, because people capital returns to Japan; due to low interest rates Japanese investors push capital out of the country to benefit from higher rates.
Forex traders use CADJPY specifically to gauge risk-on and risk-off as CAD is seen as a proxy for oil while JPY is seen as a proxy for oil. In a similar vein, AUDJPY is used because AUD is a proxy for China as China is regarded as the world’s largest manufacturer.
Regarding oil, I'm referencing Crude Oil, not the wider oil markets. Though, Crude has implications for the rest as it is the raw material as we've gone through before.