[quote=@Caits]
It just...well fine, I'll take a shot. It just nullifies the magic energy in the area, meaning that any attacks used just don't work. 
[/quote]

How about, once activated, the lacrima uses a null magic to cancel or weaken all magic in an area. However, it only can be activated for a certain amount of time and only has a certain amout of magical power to cancel, one exausted it reqirers time to recharge.