Gem Girl
A final evolution of a Rock Spirit. They can be evolved from Rock Golems into one of three types, a Magic Level Type that learns CrystalStorm, a Magic Level Type that learns CrystalShard, or a Support Level Type that learns Encase.
Gem girls have a very difficult requirement for evolution: a HP gene of 0. Even if you skip the reshaping process for a stronger base spirit, this becomes increasingly harder over time as genes in portals grow and your MC spawns stronger spirits with higher Magic. Since final spirit evolutions are rare, you can't rely on one appearing in a cave portal or showing up in the tavern hire list to recruit. If you wish to use them it's advised to evolve two of them right from the start of the game in order to overcome the low genes via breeding.
However the trouble is worth it. Gem Girls have incredible potential as tanks, surpassing even Spiked Seals thanks to their unmatched 3.0 HP growth, Regenerating onTurnStart and DrainMana onAttack to maintain it. Beyond that, they also get high growths across most of their stats and powerful spells, allowing them to excel in multiple roles. However, note that their base HP is low and their armor slot has been replaced with a misc slot, making them fragile at first.
They are also the sole source of Semen (Stone), required to craft StonePotions.
