cement bag

However, Kamijou didn’t go to punch him. Instead, he grabbed a nearby shovel. During
that time, Unabara Mitsuki began to change his knife’s angle, trying to get it to shine light
at him. Kamijou, all too aware of the sweat dripping from his palms, swung down the
shovel with all his might.
Not at Unabara, but at the bag of cement close by.
The shovel stabbed into the bag with a sharp swish, but he didn’t stop there. The gray
powder inside flew all over the place.
Unabara’s vision, his surroundings, and the sky—all of it had been blanketed in gray.
He still swung the knife, but then he realized it.
The spear wasn’t activating.
The cement powder had severed the space linking Venus and the spear. He couldn’t fire
the weapon because it needed to use the light from Venus.
A heavy object flew right past Unabara Mitsuki’s face.
As soon as he realized it was the shovel and readied himself—
“Wooohhh-aaahhhh!!”
Kamijou’s fist came from directly in front, stabbing through the gray curtain. Unabara
reflexively bent over to dodge it. There was no sense behind the action—only instinct. As
a sweat now broke out on him, he took the obsidian knife, which had become just a blunt
object at this point, and tried to bash it against the side of Kamijou’s face. But because of
his unstable stance, there was no strength behind it. Kamijou gave a roar and drove his
toes straight into Unabara’s gut.

- Toaru Majutsu no Index Volume 5, Chapter 2 Part 15