"Endurance" or whatever synonym it was, is that classic RPG skill where you die and stay at 1 HP. She burns MP to use it over and over.

I really do like the idea of draining Araba's SP until he can't fight anymore. It tied back to the much earlier episode where Kumoko almost died because she hadn't eaten in so long. She couldn't beat him in raw strength, but it is one Alpha predator starving the other one out all the same.