Description
Also sorry for any confusion for the information below, trying to explain without giving too much away again. Planning on writing a story and posting on Ao3 as I go. If I do that I will share a link the in Pinned Master Post.
THE HERO
The Hero of Termina, was not quite a hero and more a vessel created by the Goddesses to reform/house the shattered soul of their first hero. During the spread of the corruption later known as Malice the first hero used an ability that he had to seal Ganon and the corruption controlling him in a prison that he and Hylia made. Though as the years continued the Malice was able to alter the prison to it's liking and further broke apart the Hero's soul. It was during this time that forces on the outside of the prison were working to find a way to release their master so the Goddesses needed to return the Hero to one piece to stop them.
THE MASKS
The masks found throughout Termina are actually the fragments of the first hero's soul that was broken when the seal to hold Malice was initially established. It was at this point that the soul had remained broken so long it was no longer able to repair itself without outside aid, this in the form of the vessel created and sent by the Goddesses.
THE FIERCE DEITY
The Fierce Deity, as it is known in Termina, is in fact the remnants of the first hero's soul reformed, though after so long of being in pieces it is no longer able to recall it's original life or memories. With this the seal that help Malice was broken and it was able to break free. (This in the timeline is where the events of Skyward Sword begin as the seal holding demise begins weakening)