The mine number seven was a Blood Stone mine that was located deeper than the deepest mission site.
The most abundant resource in that place was a unique mineral called a 'Blood Stone'. By itself, a Blood Stone didn't have much use, but it was frequently used as a catalyst in all kinds of magical experiments. The powdered form of Blood Stone was highly sought after in the black market, since it purified and extracted magical medicine.
However, apparently, the training camp wasn't looking for Blood Stones. The ambush planned by Kevin's team was actually for the gem that accompanied Blood Stones: the Blood Garnet. As a kind of gem, once Blood Garnets were given to Master Jewelers, they were modified into all sorts of magical accessories. The jewelers did everything possible to draw out the mysterious energy contained inside of the gem, which provided the magical accessories with marvelous power.
