Is this ever explained? I assumed that you just gained all KG when you became the 10 Tails Jinchuriki, but that isn't ever said anywhere. Are we really expected to believe that Madara just had Storm Release all along and it was just never used or mentioned till then?
"After becoming the Ten-Tails' jinchūriki, he was shown using Yin Release to create lightning bolts, and Storm Release – a mixture of water and lightning-natured chakra – to create energy beams that could cut through the Six Paths Rods."