The mages of Menak are a species that are very attuned to the energies of the universe. Their Soulfire control is part of their daily lives, as their sleeping patterns had been altered by a type of magical genetic manipulation on a mass scale, called the Great Evolution.
During this Great Evolution, the Wizards, a powerful council of mages, decided to improve the abilities of their successors by limiting their sleep patterns. The randomness of dreams was their problem, and the Cronus Libra, a book of immeasurable knowledge, helped them solve the problem.
The following generation, including Miku, would not sleep to dream as their parents did. They could rest the body quickly, and enter a type of dream meditation, to improve their skills. Instead of meditating however, the children fought each other into the late hours of the night, while their parents still slept...
Shortly after those children had grown into adulthood, and the mages had mostly evolved, Xan'dros came to power. In the first of Z's journals, Soulfire, Miku expresses his disappointment in the change. While at Zeratok's home in Teuran, he explains that their capitol, Welim City, was merely a shadow of what it once was.