As you play through the mission entitled "," you'll encounter a new kind of puzzle characterized by breakable blood crystals.
If you chose to go to Treviso before Dock Town, this is the first time you'll see puzzles of this sort. These crystals effectively function as a magical power source, usually serving to keep an impenetrable wall between nosy interlopers and whatever a blood mage wants to keep secure.
Thankfully, the grand majority of them are pretty straightforward — until a certain point in the quest, that is. During this particular quest, several blood crystals must be broken to create a path to Lucanis.
However, it's an optional area — the High Security room — that provides the hardest iteration of this puzzle. You'll enter, shortly after freeing Lucanis, to find a series of barriers that scarcely conceal three rooms full of loot, and a very obvious crystal presiding over it all.
But try as you might, and the crystal won't budge; your weapon seems to bounce off it as a translucent shield appears.