The races of your mercenaries. Each race has its own stat bonuses and its own set of classes.
Human
The versatile folk. Takes the most classes; among regular mercenaries, martial arts (Swordmaster, Monk, Taoist), Berserker, Lancer and Alchemist are human-only. Combat classes get +6% to every stat, EXP +12%. Healers (Priest, Taoist) get no racial bonus.
Those awakened by the darkness deep in the tower. Damage taken -20%, all abilities boosted. Normally unrecruitable, though one freed from a contract may join through a story.
Descendants of the Dragon's Nest. Specialize in Knight/Mage/Warrior/Elementalist. HP +12%, Defense +8%, Attack +10%, damage taken -8%, Speed -6%. Regular mercenaries only seek out guilds that have passed floor 150.