The BOJ is expected to keep monetary policy steady but signal its readiness to expand stimulus again if risks to the outlook heighten.
The dollar bought 93.26 yen, not far off a 33-month high around 94.47 set on Monday. The euro fetched 125.26 , near a 34-month peak of 127.71 scaled a week ago.
Analysts say markets suspect the BOJ will stand pat until the first rate review under a new governor, scheduled for April 3-4.
"This leaves the risks that the BOJ actually does positively surprise the market. Nonetheless, it may be more prudent to wait and buy USD/JPY on the 90 handle, as the risk trade is somewhat stretched," analysts at Societe Generale wrote in a note.
They added that the surprise on Thursday could come from South Korea, whose currency has risen strongly against the yen possibly denting its export competitiveness. A Reuters survey, however, found the Bank of Korea will probably hold rates steady for now.
Since November, the dollar has soared around 20 percent on the yen, while the euro has gained about 25 percent as the BOJ came under relentless political pressure to deliver bold policies to defeat deflation.
Markets turned nervous this week ahead of the BOJ meeting as well as a G20 summit starting Friday, worried that Japan's international peers would complain about the steep fall in the yen.
A G7 statement, designed to cool international currency tensions, did anything but that after Japan said the statement gave it a green light to continue efforts to reflate its economy, but a G7 official suggested otherwise.
Summing up the frustration, the Bank of England chief on Wednesday said the G7 statement should be taken at face value and anonymous officials should not try to reinterpret it.
Markets were also waiting for Japan's fourth quarter gross domestic product (GDP) data due 2350 GMT, with forecasts centring on meagre growth of 0.1 percent in the quarter. Any downside surprise could add pressure on the BOJ to act sooner.
Volatility wasn't only confined to the yen. The euro also saw a bit of action against the greenback, first rising to a one-week high of $1.3520, before quickly relinquishing those gains to last stand at $1.3451.
Resistance is seen around $1.3530, the 50 percent retracement level of its Feb 1-11 fall.
Initially supporting the euro, data on Wednesday showed output at euro zone factories rose for the first time since August at the end of last year, a sign the single currency bloc was slowly starting to pull out of recession.
Sterling took a bit of a pounding after the Bank of England said Britain faced years of meagre economic growth and left the door open for yet more stimulus.
It struggled near a six-month trough around $1.5523 and plumbed a record low against the New Zealand dollar at NZ$1.8344.
Commodity currencies fared well with the Australian dollar rising to $1.0367, putting a four-month trough of $1.0227 plumbed on Tuesday well and truly in the rear-view mirror.
The bounce in the Aussie has also snapped a series of lower lows and lower highs in the charts, hallmarks of a downtrend after the Reserve Bank of Australia left the door open to more rate cuts early last week.