The iShares Core Japan Government Bond ETF (2561) is listed on the Tokyo Stock Exchange with a total expense ratio (TER) of 0.06%.
2561 will track the FTSE Japan Government Bond index which is made up mostly of long-dated Japanese government bonds.
Currently, the index's maturity yield is -0.09% while the average weighted duration is 11 years.
DWS has an ETF in Europe (XJSE) that tracks this exact index. It holds £797.6m in assets.