Japan has far mor serious problems than a falling yen or the BOJ. It’s population is aging faster than any in the world, Japanese youth are depressed and according to most sources and polls “without hope” for a better futur, and about 1% of young men are “shut ins” literally not leaving their rooms for YEARS. This is not a yen or trade problem.
The fundamental cause of deflation is a protracted downward trend in Japan’s GDP growth caused both by the decrease in the number of workers and declining productivity. They need a combination of approaches to end it: Monetary easing, a higher consumption tax, boosting domestic demand (especially among the elderly) bringing more old people and women into jobs to counter the decline in the working-age population, free trade, etc.