Gaara all the way. He had a demon sealed inside of him, was hated and feared by everyone, separated from his family, was told his mother hated him and his uncle (the only two people he thought loved him). Then he was forced to become an insomniac and constantly tormented by a Shukaku. He was also killed for Shukaku. Luckily brought back to life and became a total sweat heart.
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