(When we were attacked by the mobile crane near the particle engineering lab, she didn’t try to destroy the wrecking ball with her power. And with the train just now she went for the power cables buried in the ground instead of the fast-moving train itself.)

Hamazura gritted his teeth at the pain all over his body and noticed a means of getting out of this situation.

(Most likely, Mugino Shizuri’s power takes a certain amount of time to aim in exchange for how powerful it is. In other words, she’s weak to surprise attacks. She can’t deal with a sudden attack from someone.)

[...]

A bright flash swelled up.

Mugino Shizuri’s left arm was blown away from the wrist to the elbow as if it had melted. The bright light it caused was aimed for Hamazura Shiage’s face. She shot Meltdowner ignoring any kind of detailed aiming.

Toaru Majutsu no Index vol.15 ch.4 pt.7,9