Otonashi, and Yuri. Hard to choose between either. I find Otonashi's story sad, because he died trying to save people, right as he had discovered his meaning in life, then he had to let Kanade go. I find Yuri's sad, because she had to go through the deaths of her siblings... That would have been horrible!
I would think Otonashi had the worst tradgies because he Lost that girl from a illness, she was really close to him. Also dieing from the train accident was emotional too.
