Master Sword

Collect the Kokiri Emerald, Goron's Ruby and Zora's Sapphire. Stand at the Temple of Time altar and play the Song of Time. The Door of Time opens. The sword in the pedestal is the Master Sword, and a child who draws it is sealed until he is old enough to wield it. That seal is the story's act break. Adults can set the sword back to return to childhood and pick it up again to return, which is how the Spirit Temple's two halves work.

It is the evil's-bane blade and the key between Hyrule and the Sacred Realm. There is no shop price and no upgrade path inside this game. Biggoron's Sword is a different optional blade, not a plus-one of this one. The remake dresses the pedestal. It does not, in the pages I trust, add a fourth stone. If the door stays shut, you are missing a stone or you played the wrong song.

The first draw is a story transition, not a menu option for freely selecting an age from anywhere. In the original progression, clear the Forest Temple and return to the Temple of Time to gain the lesson and access needed for regular travel between eras. Put the Master Sword back into its pedestal to become a child, and draw it again to return as an adult. Child-only tasks such as planting beans, registering Bonooru's melody or visiting the Bottom of the Well can then support adult objectives. The sword is also required for Ganon's final blow, so do not treat the optional Biggoron's Sword as a replacement for its story role.