The market is getting happier with Kuroda’s comments, yen finally weakening after an hour of comments.
The ‘banknote rule’ is a self-imposed rule which caps the BOJ’s JGBs holidngs to an amount equivalent to bank notes in circulation. The US Fed, for example, does not have such a rule.
More details on the ‘banknote rule’ here: Bye bye banknote rule (for real)