Before Mad King Ashnard declared war on Crimea, Micaiah's early occupation was that of a fortune teller in Daein. During this time, she met a young boy named Sothe. They promised to look after one another forever. However, due to the fact that she was one of the Branded, the prospect of Sothe traveling with her and catching the backlash of the prejudice she would receive was unthinkable, and with that, she left him. They were reunited after the war and promised never to leave each other again.
Eventually, The Dawn Brigade unearthed a rumor that the son of Mad King Ashnard, Prince Pelleas, was secretly raising a liberation army in Daein's Desert of Death. The Dawn Brigade found an abandoned fort in the desert where Pelleas was hiding out. The Dawn Brigade helped the still-small Liberation Army defend against the attacking Begnion soldiers.
Once the soldiers had retreated, the Dawn Brigade met with Prince Pelleas and his assistant, Izuka. Pelleas recognized Micaiah instantly as the Silver-Haired Maiden, and appointed her as the vice-commander of the Daein Liberation Army. At first, Micaiah and Sothe were reluctant, but then they complied.
Once Daein was freed of Begnion, Pelleas appointed Micaiah as the supreme commander of Daein's armies.
When the Laguz alliance declared war on Begnion for Begnion's killing of a Laguz messenger and their burning down of the Serenes Forest, King Pelleas ordered Micaiah to lead Daein's armies into battle - on the side of the Begnion empire. At first, no one knew why he did this, but then it was revealed that King Pelleas had un-knowingly signed a Blood pact with the Begnion Senate, and it was the Begnion Senate that ordered Daein to eradicate the Laguz Alliance. This Blood Pact was signed on the day of his coronation, disguised as a treaty with Begnion. Despite a change in her opinion of Ike, he never accepts her for siding with Begnion.
When the goddess Ashera awoke and petrified everyone on the continent of Tellius, Micaiah's armies, and Ike's armies (who were on the side of the laguz) were petrified. The only non-petrified people were the "Chosen Ones", who had been protected by Yune the Goddess of Chaos, counterpart to Ashera, Goddess of Order. Yune had awakened along with Ashera. Ashera had petrified everyone because the leaders the countries of Tellius had promised her that they would not wage any wars for 1,000 years, but they were unable to keep their promises. Yune wanted to unpetrify everyone, but couldn't do it herself because she didn't have the power. (She had formerly been dwelling inside a bird, but then she entered and would often take control of Micaiah.) Yune (through Micaiah) explained that the only way to unpetrify everone was to go to the Tower of Guidance and defeat Ashera there. During this time, it was revealed that Micaiah was Empress Sanaki's older sister, and the true apostle of Begnion.
Micaiah went on to become the 15th Queen Of Daein at her subjects' entreaty ushering a new era of peace and prosperity after Pelleas (depending on the option you chose earlier in the game, she either becomes the queen after his death or he abdicates his rule to her willingly), being married to Sothe if they have an A support.
Super Smash Sisters
Micaiah is one of the playable Fire Emblem characters in Super Smash Sisters. She can use magic as she did in Radiant Dawn, even her Thani. When her territory is attacked, she is in command of the Daein forces. She is one of the default fighters.