As background, Japan is part of a G7 agreement not to take actions to manipulate its currency rate to gain a benefit. That’s why officials there insist their super-easy monetary policy (which is a factor that weakened the yen against higher rate countries like the US) is for domestic purposes, not to influence the yen FX rate. Japanese intervention to strengthen the yen could be viewed as contravening G7 agreements.

Ishiba’s comments need also to viewed against the pick up in (economic) threats from the US under Trump. A weak yen could (is?) be (being?) argued as a ‘non-tariff’ barrier to US products and services in Japan, prompting Trump tariffs against the country.