"Do you know of a Norse warrior called Thororm?"
[…]
"He used a magic which had the power to reduce the sharpness of an enemy's blade to zero. Thus, no attack could harm him, while Thororm's would be the only sword which could cut at the opposition."
[…]
"I have constructed a technique by which I can reduce the offensive power of any and all armaments I recognise as such to zero"
[…]
"It is effective against each weapon for ten minutes at best.”

Toaru Majutsu no Index vol.18 ch.5 pt.9