Goddess Sword

The Goddess Sword is a sword from The Legend of Zelda: Skyward Sword. The Goddess Sword's primary purpose is aiding Link in fulfilling his role as the chosen hero. When pointed skyward, the sword can charge up and deliver a Skyward Strike, a ranged attack that has the power to activate various artifacts Hylia left behind for the Hero. The sword is inhabited by a sentient being known as Fi, who aids Link in his quest.

Story
Throughout the course of the game, the Goddess Sword becomes the Master Sword, after being tempered in the Goddess' sacred flames.

The sacred flames are found in the Ancient Cistern (turns the Goddess Sword into the Goddess Longsword), the Sandship (turns the Goddess Longsword into the Goddess White Sword) and the Fire Sanctuary (turns the Goddess White Swordinto the Unpowered Master Sword).

Finally, with the blessings of the Goddess Hylia, the Master Sword becomes the fully powered True Master Sword, the "Blade of Evil's Bane".

This origin contradicts The Legend of Zelda: Twilight Princess, which states that the Ancient Sages were the original creators of the Master Sword. However, it is possible that what they meant was merely that they granted it the ability to serve as the key to the Sacred Realm.