* Nikkei logs its worst April performance in 7 years * Strategists say ETF, REIT buying a positive surprise * Investor attention turns to earnings, Europe * Nintendo tumbles after posting operating loss * Softbank surges 3 pct after big dividend hike By Mari Saito TOKYO, April 27 (Reuters) - Japan's Nikkei share average ended lower in choppy trade and closed out its worst April since 2005 on Friday, after the Bank of Japan's move to boost its bond buying failed to ignite lasting confidence among investors over the fragile economy. Stocks briefly picked up and the yen weakened after the BOJ announced during the afternoon session that it would increase its asset purchases by 10 trillion yen ($124 billion) and expand buying of exchange-traded funds and real estate-linked funds.