* MSCI Asia ex-Japan up 0.2 pct, Nikkei opens down 1.3 pct
* Yen remains firm vs dollar, euro
Asian shares nudged higher on Wednesday following gains in Wall Street overnight, with upbeat U.S. earnings and improving German investor sentiment encouraging buying of riskier assets.
The MSCI's broadest index of Asia-Pacific shares outside Japan was up 0.2 percent, hovering near Tuesday's 17-1/2-month high, underpinned by recent positive data from the United States and China.
Australian shares rose 0.3 percent as top miner BHP Billiton gained after lifting iron ore production, while South Korean shares opened up 0.3 percent.
"Given equity market earnings forecasts and valuations, we think investors are considerably more optimistic than economists and may be positioned for disappointment as the economic outlook slips back towards trend, despite a world awash in central bank liquidity," Barclays Capital analysts said in a research note.
Hopes of an improvement in the global economy led the Standard & Poor's 500 Index to a five-year high.
Late on Tuesday, International Business Machines, the world's largest technology services company reported fourth-quarter earnings and revenue that beat estimates, while revenue from Google Inc's core Internet business outpaced many analysts' expectations for the same quarter. Apple Inc's earnings release is due later on Wednesday.
Japan's benchmark Nikkei average opened down 1.3 percent after ending a volatile session down 0.4 percent on Tuesday as the yen jumped following the Bank of Japan's decision to further ease policy.
The BOJ doubled its inflation target to 2 percent and adopted an open-ended commitment to buy assets starting 2014.
The yen initially fell, but soon jumped against the dollar and the euro, posting its biggest one-day rise against the dollar in about eight months on Tuesday as markets perceived the BOJ measures as falling short of offering immediate stimulus.
The dollar fell 0.3 percent to 88.49 yen while the euro was down 0.3 percent at 117.89 yen. The dollar hit a 2-1/2-year high of 90.25 yen on Monday.
Many still believe the yen will resume its recent downtrend, seeing the latest rebound in the Japanese currency as a correction to its rapid and sharp decline over the past two months on expectations for aggressive BOJ monetary easing.
Overall global market sentiment has been improving as worries over U.S. budget woes and euro zone's debt financing have eased.
Republican leaders in the House of Representatives said they aim to pass on Wednesday a nearly four-month extension of the U.S. debt limit, to May 19
German ZEW investor sentiment rose sharply for a second consecutive month in January to its highest level in more than 2-1/2 years.
Foreign investors piled into Spain's new 10-year bond on Tuesday, allowing the country to raise around 14 percent of its 2013 funding target, while major sovereign debtor Italy has raised around 10 percent.
U.S. crude was up 0.1 percent to $96.78 a barrel.