You can gain this ability at any time when creating your character or leveling up, so long as you meet its prerequisites.
You gain the ability to cast Spells, Techniques, and Rituals.
You gain +1 free rank of the Elemental Affinity Feat.
Spells you cast are always Dark Magic.
You use the higher of your Charisma or Intelligence for your spellcasting attribute.
Dark Magic spells use Verbal components for their casting and Somatic components for their Metamagics.