The Mu'hari are one of the castes of the Polaris society; their name translates literally to "servants of all". They were created after the Polaris Civil War, in which Iusia, the leader of the Nil'kemorya, declared war on the other castes. The Mu'hari serve in virtually every capacity, as they must train to help whenever asked, and they are not allowed to refuse. They are spies, scientists, engineers, pilots, diplomats – any area of life that exists among the Polaris has at least a few Mu'hari engaged in it.

To become a Mu'hari, a young Polaris must first have failed at joining another caste. Only then will they be assigned to the Mu'hari caste. Because of this, the Mu'hari have a great deal of shame, a burden that they cannot relinquish.

The Mu'hari make heavy use of the Polaris Zephyr starship, which enables them to travel great distances across space at high speed, undetected by possible adversaries.