The yen gained in volatile trading and stocks and bonds tumbled in Tokyo after the Bank of Japan said it would take a more flexible approach to lower long-term yields, while stimulus hopes sent Chinese stocks up for a week. The Bank of Japan maintained ultra-low interest rates but said its 10-year government bond yield target of 50 basis points on either side of zero would be a "guideline" rather than a "hard cap." The Nikkei stock average fell 2%. Banking shares (.IBNKS.T) surged 4% to an eight-year high on the prospect that the change could mark the end of Japan's ultra-easy monetary terms and pave the way for higher interest income.