Possibly: Bank of Japan raises (or maintains) interest rate today or in the future, causes unwinding of the carry trade, which in turn causes over-leveraged ban

Possibly: Bank of Japan raises (or maintains) interest rate today or in the future, causes unwinding of the carry trade, which in turn causes over-leveraged banks (hello UBS/Credit Suisse) and hedge funds (hello Citadel, Susq, etc) to close/cover positions for margin, causing a chain-reaction and big crash. Again, basically the same root cause as 2008: lack of regulation, lack of enforcement, institutions "investing" in dogshit wrapped in catshit that shouldn't have exited in the first place, crash.