After a week of rapid increases, yields on Japan’s 30- and 40-year government bonds dropped more than 10 basis points in late trading on Friday.

Treasury yield has grabbed the lion’s share of attention lately when it comes to signaling how the U.S. fiscal outlook is rattling investors. Yet there’s another less-talked-about factor weighing on sentiment that is coming from overseas: the tumultuous rise in the bond yields of Japan.

Japan's super-long government bond yields have spiked to record highs, as mounting political calls for tax cuts and big spending draw investors' attention to the country's fiscal woes. The rise in yields complicates the Bank of Japan's (BOJ) quest to wean the economy off a decade-long stimulus programme including by slowing its huge bond purchases.