For an all white mage run, four mages can FADE chaos before he uses cure 4 using a small amount of trial and error. With one white mage your only hope is to either MUTE him (1/256 chance) and then slowly stab him to death with the masamune and hope he doesn't throw a lucky hit (at level 50 this probably wouldn't ever happen). You can also as shown here just randomly present the bane sword until he bites it (1/256 chance again).
This means that this guy is astonishingly lucky to capture this in a video. Or he silently abused save states.
I'm almost positive this guy's using save states on an emulator. You don't buy SOFT or ARUB or HEL3 on a solo white mage run. (In fact, you don't buy SOFT or ARUB at all.)
This might be the greatest video in the history of human civilization but there's no way I'm ever going to find out because 3 seconds of this dipshit's voice made me close the window so quickly I nearly hurt myself.