Crystals, Lots of Crystals!

In the darkness of the Eternal mines, the sound of a pickaxe striking metal echoed over and over. 

— Clang!— 

— Clang! Clang! — 

— Clang! Clang! Clang!— 

— Thud!— 

The Demon King's student had defeated yet another group of monsters. Jack's knowledge had made Derek the bane of these creatures. 

The "Sword Genius" barely ever touched his sword anymore. He only used his pickaxe. He used it so much that it was about to shatter from the wear. 

He showed incredible courage, so much that Jack actually couldn't get rid of him even if he tried. 

"I'll stay by your side, Master. I may not be immortal like you, I may not be wise either, but I won't let you struggle alone!" His foolish student had declared. 

Jack wasn't sure whether to be proud or facepalm. What was up with that level of devotion?! Had he raised affinity that much?!