Her Personal Name is Chaika (チャイカ, Chaika?).
Lerche is the first of the Sirins developed by Viktor Idinarohk. She serves in the 1st Armored Corps of the United Kingdom of Roa Gracia as an Alkonost pilot, as well as Vika's personal attendant and retainer. She was created in the image of Lerchenlied, Vika's deceased milk sister.
As a Sirin, Lerche's body is entirely mechanical despite being described to be very humanlike. She is said to have the golden hair and green eyes of an Emeraud, possibly the same traits that Lerchenlied once had. She has only been shown to be wearing the Sirin uniform, consisting of a dress similar to a scarlet tunic with the front side exposing a navy garment.
Lerche is someone with a calm visage and witty humor if necessary, almost always directed towards her lord. As a Sirin, she does away with many feelings that humans might have regarding the preservation of her life. She does occasionally possess an aggressive and mocking side when especially peeved, such as her conversation with Shin regarding humans on the battlefield.
Lerche hides a strong jealousy and contempt upon human soldiers. She's almost insulted by how they could throw their lives away on the battlefield, in an age when warfare had surpassed that of humanity's capabilities. She feels that humans could retry and redo the things in life that they failed at, but the dead cannot do the same.
This is due to her strong regrets of not being able to fulfil her goal as Lerchenlied's replacement towards Vika. Unlike the other Sirins, her base personality and memories were never deleted, as they weren't there during the time of the brain scan. She feels that if her personality and memories were not of Lerchenlied's, then she never had any connection to the girl to begin with. This troubles her, as she believes that she will never meet Vika's expectations as an attempt to preserve his memory of Lerchenlied.
Lerche was created as the first Sirin, a weapon with the intended use of being the United Kingdom's spear against the Legion. It began when Lerchenlied had died when she accompanied Vika to his first battlefield. Once again, just like his mother, Vika attempted to preserve her into an artificial intelligence using his Amethystus abilities. He succeeded in using Lerchenlied's brain structure to create Lerche in SY 2144, and in the process invented the base process of creating the Sirins.