User blog comment:Xilinoc/Everything but the Rain op. 9 - "June Truth"/@comment-6963992-20130508204040/@comment-5551986-20130508234555

He probably didn't use Getsuga Tenshou because White didn't give him the chance. Although the attack he opted to use was incredibly powerful. Getsuga Tenshou is a ranged attack. He was not close enough to attack the inner world mask.