Two-year yield as the short end: the Ministry of Finance's daily table starts at one year.
The ten-year minus two-year Japanese government bond yield from the Ministry of Finance's daily reference table.
Threshold source: Yield-curve rule with the two-year as the short end; the Ministry of Finance publishes no three-month yield. How thresholds are chosen
Decades of yield-curve control make the historical record of this spread a poor guide to what an inversion would mean now.