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MiinU
Since: Jun, 2011

It's the final battle. The hero has been going at it with the villain, they're losing bad. All out of options, barely any strength left, he's about to pass out. But he remembers, he's doing this for his family/friends/the world, and gains enough power/overwhelming power to get up and defeat the villain.
I'm sure this is an obvious one, I just can't articulate it enough for the search bar :/