Soul Crystal

The Soul Crystal in the Dungeon Crawler Carl series begins as a C-Grade amber gem in Book 2, floating and emitting golden tendrils to harvest soul energy for recharging swordsmen guards amid the dungeon's brutal carnage. By Book 3, these crystals power ghoul generators but catastrophically overload and explode from mass deaths, leaving inert marble-sized remnants. Evolving into a more utilitarian F-Quality purple-hued gem by Book 4, it is encased in a clamshell device to regulate power for Carl's dirigible house balloon, rechargeable through kills and displaying a dull purple glow rather than vibrant blue.