The Gilded Sword is an upgraded version of the Razor Sword and is only attainable after acquiring Gold Dust. While the Razor Sword deals merely twice the damage of the Kokiri Sword and only lasts for 100 strikes, the sword will not break and is three times as strong as the original blade. Additionally, the Razor Sword cannot be taken back in time. The Gilded Sword, however, can be taken back in time.
Obtaining the Gilded Sword
Link can enter the Mountain Smithy and ask to have the Kokiri Sword upgraded for a fee of 100 Rupees. After doing this, Link must venture to the site of the Goron Race while wearing the Goron Mask and win the race. When this is done, he will be rewarded Gold Dust, which can be used to upgrade the Razor Sword to the Gilded Sword.
NOTE: In order to complete this side-quest, Link must acquire the Razor Sword on the Dawn on of the Second Day or he's not able to obtain the Sword due to time restriction.