Amid a storm of volatility in Japanese stocks, the Bank of Japan has kept the bond market a pool of serenity.

The Nikkei Volatility Index surged to 48.99 on Aug. 26, the highest since the disasters of March 2011, and was at 31.92 on Tuesday.

Since China's yuan devaluation last month, a similar gauge measuring fluctuations in Japanese government bond futures has averaged 2.69, below its one-year average of 2.90. Turnover in the JGB market last month dipped below the average over the past year, while Topix index volume surged to the highest in two years.