chain prediction

Kamijou heard the sound of the chain.
The chain attached to Vento’s tongue drew an arc from right to left as she moved. Vento
forcefully swung the hammer vertically so it scraped along the chain.
Orange sparks flew out.
(!? For a while now...)
A weapon of air blew the sparks away as it curved from the right to the left.
(...the attack’s direction has been different from the hammer’s!?)
It almost seemed to follow the trajectory of the chain attached to her tongue.
(This pattern!?)
It almost seemed to be guided by it.
“You don’t mean... The cross on that chain!!” shouted Kamijou as he crushed the wind
weapon with his right hand.
Vento laughed in response.

“Oh, did you find out!?”
The long chain with a cross accessory attached freely drew vertical and horizontal
trajectories through the air. Whenever Vento swung her hammer so it scraped across the
chain, a weapon of air would fly along the same route as the line of the chain.
(Damn it! It’s hard to defend against even when I know how it works!!)
Without meaning to, he would instinctually react to the trajectory of the giant hammer
that was producing shockwaves. But the hammer and the chain moved differently. She
would swing down from above, but the chain would be drawing a curving line. She
would swing the hammer horizontally, but the chain would move upwards from below.
The motion of the attack and the direction in which the actual attack flew were different.
That slight visual deception slowed his reaction time and threatened to have his body
sliced in two.

- Toaru Majutsu no Index Volume 13, Chapter 7 Part 7