Katsuro's AI is random, and at level 3 and above he gains the ability to shoot before every slash.

This is very annoying because the full cycle takes roughly four seconds, and this process can't be stopped by attacking him with the katana (although if done quickly enough, that can be used as a last resort defense in case your mess up your block timing). The worst possible RNG would have him shoot 3 times consecutively, meaning 12 seconds lost, which can easily cost otherwise good runs.

However, it's been discovered one can force him out of the animation early by Dragon-Slashing in his general vicinity, forcing him to initiate a slash attack (including the triple dash slash at max level, so keep your guard up). It's recommended to use block right after exiting the Dragon-Slash because he will immediately dash towards you. This doesn't guarantee he won't use his gun again later in the fight, but it can save time you from getting bogged down with this one attack.

Video of it in action:

I'd recommend always leaving at least two adrenaline bars full when entering his fight past 200 kills, to guarantee you have at least one dragon slash available to counter his gun.