Fi

Phi is a character from The Legend of Zelda: Skyward Sword.

Story
Phi is a mysterious, blue-hued figure and the humanoid representation of the Skyward Sword. Phi aids Link in traveling from his hometown of Skyloft, a city in the clouds, to Hyrule. Phi can sense items and makes sounds as Link approaches important objects like keys. It has also been confirmed that it will transform into the Master Sword at some point in the game.

Interestingly, Phi resembles the Queen of Fairies from The Legend of Zelda: The Wind Waker, as well as Prince Ralis from The Legend of Zelda: Twilight Princess.