Spoilers for Fate/Zero.
As I’ve said many times before, Rider and Waver are my Fate/Zero. I really do not care about the stories of any of the other characters. Most of the others in this show are a bunch of deep-voiced, brown haired, stoic dullards. Kirei, Kitisugu, even characters like Saber, Lancer and Irisviel were all boring as hell. I do rather like Gilgamesh though. He is the ultimate in self-important stuck up pretty boys, so convinced of his own fabulous that even casting his eyes upon mere commoners is beneath him. He is the hardest man to earn any respect from in the entire universe.
Let’s rewind back to the start of the story when Rider was trying to grill Waver about what he was going to wish for if he got his hands on the Holy Grail. All Waver wanted was respect. Not world domination or lots of money or a harem or anything. Just respect, which Rider scoffed at. Rider said that he should wish for something he had no control over, like getting taller. Rider saw in Waver that he could be a respected person if he just applied himself.
The beauty of the Rider/Waver storyline is that he never needed to win the Holy Grail war. By simply summoning Rider and living under his hard fatherly hand of tutelage, Waver would grow into a person worthy of respect. They were never going to win the war, because it had no purpose in the narrative. Before they went out to their final battle, Waver officially released Rider from his contractual binding, which is the exact point Rider considered Waver an equal.
And so Rider was killed by Gilgamesh. Inevitably too, as in order for Waver to grow any further, he had to leave Rider and explore the world himself. But right after Gilgamesh killed Rider, he strode towards Waver in all his pompous arrogance with what appeared to be the intention of killing him. You can’t do that! You can’t kill Waver right at the moment his narrative arc has come in full circle! That would be the biggest dick move ever. I know you like killing people Butcher Gen, but this would be just morbid depression for the sake of it.
But no, Gilgamesh didn’t kill him. Waver faced him down and earned Gilgamesh’s respect. The hardest man in the entire history of mankind to impress, Waver had done it. He didn’t need the Holy Grail. His wish had already come true.