Djinn
and Tonic
Honestly my theory on the Master sword is that it is an inversion of Demise's sword, not the other way around. Demise and Ghirahim came first and the master sword was created later. It is not specifically explained but we are led to believe it was a few hundred to a few thousand years after Demise was defeated and sealed away. Because of this I have always assumed that it was not Demises's sword that was an original design and the master sword was made as a mockery of it for mortal Hylians to use. Demise's sword has a pointed spiky hilt, well the master sword is smooth. Demise's had a triforce, the master sword had an inverted triforce. It seems that it was formed in absolute defiance of him. As if Hylia or the Gods concluded that their weapon of choice for the hero to use against Demise would not only be designed to defeat demons, but would be visually offensive to them as well.