Fi

Fi is a major character in The Legend of Zelda series.

She appears as the deuteragonist in The Legend of Zelda: Skyward Sword a minor but pivotal character in The Legend of Zelda: Breath of The Wild. She is the spirit residing in the Goddess sword, Ghirahim's good counterpart and the first companion to any incarnation of Link.

Skyward Sword
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Breath of The Wild
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Hyrule Warriors
Fi appears as a supporting protagonist in this spin off game as well as a playable character.

Her rivalry with Ghirahim is immensely played up in this game and she is shown to be an expert battle strategist and leader capable of helping lead armies of several heroes and in the long run defeat Ganondorf.

Super Smash Bros. Series
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Personality
Fi is a very intelligent and powerful sword spirit who is immensely loyal and helpful to her allies. In spite of this however she is completely incapable of registering and expressing human emotions although is capable of detecting them in others such as Ghirahim and Link.

Fi in spite of her extreme apathetic nature and inability to feel emotions is always fighting on the side of good