Why does USD/JPY goes down when USD strengthens and vis-versa ?

As for most US currency pairs, it’s pretty straight forward in terms of the price action as a result of the strengthening of the US dollar, i.e., a strengthening US dollar would in turn drive the other currency weaker against the US dollar. So, why does USD/JPY goes down when USD strengthens and vis-versa?

This is actually a natural behavior of the USD/JPY pair. One way to think about the effect of the US dollar on the JPY is to think about risk-trade, ie, risk-trade and risk-aversion.

Let us examine a few basic concepts. Firstly, a large majority of the financial instruments are denominated in the US dollar currency, and Japan provides the cheapest loans. Therefore, when the risk appetite increases, more JPY is sold against the USD so that investors can put this into “riskier” assets such as equities, commodities, et al.
On the other hand, when investors become risk-averse, they quickly want to come out of the riskier assets by selling off their assets and in-turn buy back into JPY, thus strengthening the JPY. For example, a major sell-off in the S&P500 or DJI would send the USD/JPY pair lower.
The same concept applies to the other currencies against the JPY. You may have noticed that any major worldwide risk event sends the JPY stronger against all major currencies.