It's been ten years since they last saw each other, and now they're back on the battlefield. The Professor is still trying to figure out what the heck is going on. He's not sure if it's related to his work on the laws of robotics or to his discovery of the electric current in the human body. He also doesn't want to cross the line and say that he's changed his mind about using the current in his body to fight off the icicles. The professor says that the fight has ended, and that the ice around Yu's body is starting to grow larger and larger. Yu can't even land a blow on her anymore, because she's using the ice to defend against his speed. He wants to use the current to attack her again, but the professor says it'll only increase his speed, which will make his body even more tired. Yu wants to know why his speed isn't getting faster, and the professor explains that the speed increase is called 'thunder speed'. It uses the current from the armor to stimulate the cells in the body. The problem is that the cells are only able to do so for a limited amount of time, so if you want to increase their activity, you'll have to keep them busy for a long time. So, if you're going to increase the speed of your body, you need to keep the cells busy for long periods of time. That's why the professor calls "thunder-speed": it uses electricity to stimulate your body.