I just thought it was an anti Saika Sword considering how confident he was. Kinda like how Shirou was to Gilgamesh despite how powerful gilgamesh is, he’ll never win against Shirou/Archer’s reality marble.
They coulda maybe worked together instead of him one shotting her since he was that strong.. now its a guess game on whats gonna happen in the future.So he thrusts it right in her without...
...any plan on how to stop the catastrophe she was trying to stop?