As Yamatai evolved into the Yamato court and eventually set out on the path toward becoming a centralized ritsuryō state, the miko—originally rooted in local folk traditions—were gradually absorbed into the state system.
This integration had already begun during Himiko's lifetime, as she worked to unite the various warring tribes.
The Gishi Wajinden (Records of Wei: Account of the Wa People) records the following about Himiko:
"Formerly, the country had been ruled by men for seventy to eighty years. The land fell into disorder, and warfare persisted for years. At last, the people united in appointing a woman as ruler. Her name was Himiko. She served the way of spirits (kido) and was able to mystify the masses. Though already advanced in age, she had no husband. She ruled with the help of a younger brother. Since becoming queen, she rarely appeared in public. She was attended by a thousand maidservants, and only one man served her food and communicated her words. Her palace, towers, and enclosures were built in solemn form and guarded day and night by armed men."
From this, we gather that Himiko was already of considerable age at the time. She had no husband; her brother supported her political duties. She kept herself secluded, rarely seen by others. Although she was attended by a thousand women, only a single man was permitted to approach her, delivering her meals and relaying her commands.
Of course, the presence of this one male attendant and her younger brother is intriguing—but what's even more striking is the mention of "a thousand maidservants." Who were these women? It seems unlikely they were merely attendants or ladies-in-waiting.
After Himiko's death, a male ruler took the throne, but once again the country fell into turmoil. To restore order, a new miko-queen named Toyo (Tōyo) was chosen as Himiko's successor. There appears to be no blood relation between the two.
This suggests that a structured organization of miko had already formed around Himiko. With age, her spiritual abilities may have diminished. While she still secluded herself for rituals, it's likely that other miko were stationed close by—receiving divine messages in her place, contending with one another in spiritual influence.
Out of this group of miko, the next "Himiko"—that is, Toyo—emerged.
Later, under the Hime-hiko system of governance, the sister or daughter of the Great King (who had not yet acquired the title of "Emperor") was appointed to oversee sacred rites as miko-queen. But was she truly endowed with spiritual powers like Himiko? Or was she merely a ceremonial figure, like the saiō (Imperial Princess Priestess) of later times who served at the Ise Grand Shrine, enshrining Amaterasu?
In either case, beneath her, there must have been a host of rival miko, each competing for influence. The image of the miko as a natural-born "primitive shaman" arising spontaneously from within the community was, by this stage, already fading from view.