TROPHY NAME -------------------- Eye of Truth
TROPHY DESCRIPTION ----- Made 15 weak-spot attacks.
Very straightforward trophy. I got it without even taking note of the fact that this trophy is a thing. A weak attack is when you attack an enemy with an element they're weak to. When you damage said enemy with their weakness, the damage numbers will show up in yellow, instead of white. (I assumed it was a critical hit)
You do not need to use only skills to get this trophy. Weapons have types to them, too. For example, I have the Envy Blade for Kanata, which I purchased in the capital. It has a thunder element to it, which mechs from the ruins were weak to. You only need to perform a weak attack, it doesn't have to be a kill. 15 will come naturally.