It is estimated to be created sometime between the Hong Kong incident and Amalgam's first assault on Merida Island, where it was deployed for the first time on the Western Pacific Fleet SRT's ASes.
The Fairy's Eye is a sensor that can be retrofitted to the optical array of Arm Slaves, notably 3rd Generation types such as the M9.
It produces a spectral overlay on the AS operators display console similar to a thermal imaging camera, giving a graphical representation of the strength and extent of coverage that a Lambda Driver has over its local Arm Slave, including where the focus of its pilot is. It also displays the energy fields, which were previously invisible to opposing ASes.
This provides a tactical advantage to the operator of a Fairy's Eye equipped machine, enabling them to find "blind spots" in Lambda Driver equipped machines. As a result, the Fairy's Eye operator has an opportunity to exploit gaps within their opponent's focus, preventing them from using the Lambda Driver to generate effective protective energy fields, and offering a chance to inflict damage.
When in use on an M9, the Fairy's Eye cannot be utilised together with the ECS due to the power requirements.
The first use of the Fairy's Eye was during the Amalgam assault on Merida Island, instigated by Leonard Testarossa. Mithril detected in the incoming assault party, notably led by three Behemoth type Arm Slaves (similar to that encountered in Tokyo).
Unknown to Amalgam forces, Mithril had adapted the Fairy's Eye to SRT M9s, and the new technology allowed them to develop a high-risk defensive strategy based on generating and attacking blind spots on the Behemoths, leveraging from Kurz's previous experience in damaging the type through surprise means. Through a combination of Mithril diversionary attacks and sniping attacks from Weber's 76mm Sniper Rifle, two of the Behemoths were destroyed before the remaining Mithril forces retreated on the Tuatha de Danaan.
The Fairy's Eye was also used by Mithril SRT members to attack and defeat Codarl and Eligor type ASes during battles in San Francisco, Mexico and Afghanistan (Helmajistan). Amalgam forces, particularly Codarl operators, were not aware that Mithril had created a countermeasure to Lambda Driver use as all pilots who encountered it were killed.