"But they—the Sirins—are dead. They're merely imitating humanity, technically without personalities of their own. The Sirins are mass-produced, and they're replacable." ― Viktor Idinarohk to Vladilena Milizé.
A Sirin (シリン, Shirin?), dubbed the Artificial Fairy (人造妖精, Jinzou Yousei?), is a pseudo-artificial intelligent being developed by Viktor Idinarohk. Once a soldier that has volunteered to donate perishes on the battlefield, their digitized brain structure would be reproduced via artificial cells. Their memory is then wiped and a pseudo-personality is installed, before transplanting the cells into a mechanical body visually identical to that of a human. No matter the sex or gender of the donor, the Sirins are all feminine in their personality. Due to them being a product of the dead, Shinei Nouzen can hear their cries of wishing to pass on to the afterlife.
The Sirins were developed after the Mariana Model AI based on Vika's mother. Much like his previous artificial intelligence, the Sirins were created in order to preserve the life of someone close to him that he had lost. The first ever produced Sirin—Lerche—was based on a girl named Lerchenlied, Vika's milk sister. She had died when accompanying Vika to his first battlefield. Unlike the other Sirins, she never had to undergo memory deletion, as her memories were not present even during the brain scan.
The memory deletion procedure became necessary during the creation of future Sirins, as the brain structure would simply collapse and never start up. Once Vika had perfected their method of creation, the Sirins were mass-produced for the purpose of combating the Legion. The Sirins were deployed on the battlefield with the semiautonomous Alkonost, soon becoming the bulk of the United Kingdom's Armored Forces.
The Sirins, with the sole exception of Lerche, are able to be backed up and redeployed onto the battlefield even after their mechanical bodies are destroyed, making them an expendable force. The Sirins are reckless in their way of fighting, much like the Eighty-Six. The Alkonosts which they pilot are not built with their safety in mind, and commanders can order them to execute commands that would be considered inhumane to a normal soldier.
The Sirins are accompanied by Handlers carried inside a Barushka Matushka. They act as their tactical commanders and battlefield supporters. Some of the Handlers cherish their Sirins dearly, going so far as to curse the members of the Eighty-Sixth Strike Package when the Sirins had to be sacrificed for their sake.
- The word "Sirin" is inspried by Russian myths, where a Sirin is a half-woman, half-bird monster.