Fi (Total War)

Fi is the spirit residing in the Master Sword, the weapon hand-crafted by the Goddess Hylia for her knight Link to use.

The Return of Sulkaris
Fi is the second attempt of Hylia and the Sages at the ultimate weapon following the failure of the first one, Ghirahim. With the Master Sword successfully completed, Link is unleashed upon Hyrule.

In-game
Fi (and her counterpart Ghirahim) are the single most powerful units in the game, and act as veritable one-man (or genderless robot sword) armies.