Wolf's Rain was the most depressing ever.
The wolves, in their search for paradise, find themselves within a snow covered, barren wasteland, which was to become paradise. The villain, Darcia, determined to go to Paradise himself, goes there as well. The wolves fight against Darcia, but he is a wolf at least twice their size, and all are killed. Kiba, the white wolf is the last one alive, and attempts to fight him off, but fails. In the end, Darcia attempts to enter Paradise, but since he is not truly a wolf, and is impure, he is destroyed. Only his eye remains. The flower maiden then dies of her injuries and changes into seeds of the Lunar Flower, the sign of Paradise. The White wolf, barely alive, attempts to disperse these seeds, but soon succumbs to his injuries and collapses... The ice below him begins to melt as paradise is born, and he sinks down, eyes fixated on the moon above...
... However, Darcia's eye, which remained behind, contaminated the new world as it was born. It spread and infected the lunar flowers, and they died. Fast forward, we see the wolves once more in the realm of humanity, as they were in the beginning of the series, back to the starting point. Paradise was not born.
I cried.