Ichirei Shikon (一霊四魂) was a prediction search engine, originating from the Island Nation and created from the brains of five people, which attempted to defeat the world powers with the Amaterasu weather control system.
Ichirei Shikon is a Shinto theory according to which the spirit of both kami and human beings consists of the direct spirit and four souls. The four souls are the the wild soul, the harmonious soul, the wondrous soul, and the happy soul. According to the theory, each of the souls making up the spirit has a character and a function of its own; they all exist at the same time, complementing each other.
When questioned about its nature, Ichirei Shikon states that it's nothing more than a prediction search engine created from the brains of five people. Unlike an AI, Ichirei Shikon does not think for itself; it merely responds to questions and the surrounding circumstances by putting together strings of text and returning an anticipated answer. As the term Ichirei Shikon suggests, the pathway to reach that answer is fairly complex and multiple answers are sometimes reached.
In other words, it simply gives the answer the person would eventually think up on their own, shortening the process, but not adding in anything new. During its conversation with Ayami, she felt like she was talking with Yamato despite the fact he had been dead for over twenty years. Ichirei Shikon sometimes predicted her questions and displayed the answer before she asked.
One of its creators, Yamato, was the husband of Ayami Cherryblossom who died over twenty years before the events of the series. In the past, Ichirei Shikon caused trouble in the Island Nation, allowing Ayami and her family to escape from the country without being assassinated because of her classified knowledge of Objects.
Ichirei Shikon caused a self-defense PMC from the Island Nation to rebel, starting a civil war in the region. Under its instructions the PMC took over the Ame-no-Darin and built an Object known as Ame-no-Uzume to act as the control point for the Amaterasu weather control system.
During the 37th's battle with the Ame-no-Uzume in the New Caledonia District Ichirei Shikon contacted Ayami, seemingly ignoring the military network. During their conversation Ichirei Shikon revealed to her its true nature as a prediction search engine. It also stated its goal was simply achieving the victory over the world that had been stolen from the Island Nation when they created Objects. However, Ayami noticed that Ichirei Shikon had given her an obvious hint to defeat it, suggesting that in the end Yamato might had not been able to make up his mind and instead decided to hand the decision to his wife.
After the Ame-no-Uzume was destroyed, Froleytia's superior informed her that Ichirei Shikon was being made to take the responsibility of the incident, and that it had already been purged by the Capitalist Corporations. Ayami deleted the chat logs of her conversation with the prediction engine, erasing the last vestiges of Yamato and her lingering regret.