Message contains spoilers.

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The Link in this game is just a regular kid who wants to save his sister, but it evolved from there until it was realized that he was the reincarnation of The Hero of Time. It is when the Triforce of Courage appears on his hand that you realize this. And with Gannondorf stating that he is The Hero of Time reborn

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The shield in the game could be the Hero of Time's shield quite easiley. Remember he is still alive after OOT and MM, so maybe at some point he got a new shield.