30-40 kilometer sword

Kamijou was one of the closest ones to the scene, but he did not know that a giant sword
thirty or forty kilometers long had been swung down. After all, the base of the sword,
was so far away it was almost disappearing off the horizon. A sizzling sound could be
heard coming from the sword. It wiggled back and forth and then slowly lifted up much
like an axe being pulled out of a large tree.

“With something this big, aiming can be a pain,” Fiamma said cheerfully.

Kamijou trembled as the giant sword that could split a mountain range in two was once
more casually lifted up.

-Toaru Majutsu no Index Volume 20 Chapter 2 Part 6