were you thinking 'ichigo ichie e?' - 'one encounter, one chance?'
maybe not, but just thought i'd throw it out there...
This phrase applies in the narrowest sense and has much the same meaning without being specific to sword. But in the larger sense it refers to the fact that each instant of ones life that passes and one can never get it back. So whatever you do, you do with complete "makoto" or sincerity because there are no do-overs.
Jun's phrase is more focused and is closer to the one cut, one kill meaning.