The Master Sword's Power
As part of the Trail of the Master Sword quest, Link will travel to the Korok Forest. After heading down the Deku Tree Chasm and defeating the Gloom Spawn and Phantom Ganon, Link can return to the Great Deku Tree where he will see the memory.
The memory can be found at The Great Deku Tree, after clearing the Gloom Spawn at the bottom of the Deku Three Chasm.
"Link recovers the Master Sword in the Lost Woods after it's been restored. Zelda is astonished to learn from the Deku Tree that the Master Sword will become even stronger when flooded with sacred power."
The memory showcases events that occurred just prior to the events of The Awakening, the opening cutscene at the start of the quest. Link and Princess Zelda travel to the Korok Forest where Link acquires the Master Sword. Princess Zelda is amazed that the Master Sword has the ability to heal itself, no matter how damaged it becomes. The Great Deku Tree says that the Master Sword will continue to gain strength if it is bathed in a sacred power. The stronger the power, the more powerful the sword can become.