Another key element of "Battle Realms" is the Yin/Yang system. Each army obtains points of Yin or Yang when in combat, depending on their moral alliance to the forces of light or darkness. Hero units, or Zen Masters, require Yin/Yang to be summoned and increase their damage. Yin and Yang are also used by structures in the faction's base for military upgrades. The rate of Yin/Yang growth depends on the strength and flair of the army and how far they are from the main base.