An investor in Japan had to hedge for currency exposure if he/she wanted to invest in US Treasury market. That hedging costs used to eat out any yield from US bonds, making Japanese investors uninterested in US bond markets.
With the rise in US bond yields, that picture has changed! Investors in Japan can make real yield even after hedging costs. This makes USDJPY pair vulnerable to upside moves!
If you a forex trader, USDJPY pair offers enormous opportunities in the LONG side.