User blog comment:Xilinoc/Everything but the Rain op. 4: Dark of the Bleeding Moon/@comment-5198194-20130328001941/@comment-7286548-20130328215514

Well we do know how sharp Ichigo's and Isshin's Getsuga Tenshou are, maybe "burn" means the vibrations of the blade at a high speed, you know how a blade heats up when its vibrated at certain speeds right, it may explain the reason for their sharpness though this is only my personal opinion