Time decay. With less than three months left, and the BOJ having been in a hiking cycle, there would need to be a major shock for rates to go negative in the relevant timeframe. The appointment of a new PM perhaps dials up the temperature on that, but the base rate on a Covid-level crisis is low. And a big but slow-moving crisis like the GFC would, I expect, take too long to get BOJ to negative rates quickly. If I were to worry about a specific, obvious risk, it would be an escalation of trade tensions with the US. There is an important top-level meeting due a few weeks from now. But even if such a crisis happens, it might not result in negative rates this year.

Any estimate of an extreme, sudden shock will necessarily be low confidence, but I'm guessing in the region of 1%-2%.