Ultraman Ace: S1 E25 - Pyramid Is A Terrible-Monster's Nest! Ultraman Ace
A pyramid suddenly appears in the middle of an elementary school playground. One by one, the children drop to the ground after inhaling the red gas that jets out from the pyramid. A girl named Michiru is the only one left standing. It turns out that she is an agent of the Alien Orions, beings who once ruled planet Earth.