Being ready for anything doesn’t mean planing for everything, that’s impossible. They’ve likely planned for the obvious. They also have the resources ready to go to adapt to an unexpected situation.
A swordsman is t ready to block every conceivable blow. They, instead, prepare to react. If it’s a known attack, they can fall back on a planned move. If it’s abnormal they can react by improvising, using the skills they already have.
Oh, and the swordsman’s issue isn’t the lack of plan, improvisation is a key skill. The issue of the inability to read the opponent. It throws their instincts out. E.g. an attack looks like a faint, since it would leave the attack open to a lethal counter, even if it connected. An expert would never use that. A beginner might.
Don’t commit war crimes. Instead, be the reason they became crimes!