Based on the proposed "Sakurai Theory" from the Special Disaster Response Team Division 2's own technology expert, Ryōko Sakurai (in actuality Finé, who had possessed Ryōko's body by the time), "Symphogear" is the name of a special, counter-measure armor that was created through the phonic gain of unique relics. Having been developed with the use of multiple theories and technologies outside the relm of traditional science it is currently the only existing weapon known to stop the world-wide disaster known as the "Noise," however to avoid conflict with current constitutional laws its existence has been completely hidden to the public.
Able to respond to the synthetic vibration resonance created by the fighting spirit of the user, the Symphogear's greatest trait is its internal functionality to play a certain melody. By synchronizing that melody with the user through song, the Symphogear displays an incredibly high rate of battle potential.
Although the armor is able to absorb damage during battle, any sort of disruption of the song will result in a temporary dampening of its battle potential. At the moment, this is the only weakness that has been observed in the Symphogear system.
Most Symphogears has a ultimate form called X-Drive form, where most of its limiters are released, giving the user immense power, capable of destroying a great amount of Noise at once. Depending on the number of limiters released, the armor may manifest in different forms under X-Drive mode.
See: Symphogear Users
Over the course of the series, each user's Symphogear has gradually changed and evolved with time and usage.
In fact, the Symphogear system has 301,655,722 different varieties of locks applied to it. Depending on the user's level of ability and their personal battle style, there is a systematic progression of phases that the user will go through to release the locks.
The purpose of this setup is to adjust the Symphogear to the user's individual preferences, however it is also in place to reduce the strain put on the user's body as much as feasibly possible. In order to achieve this, and give the user a greater mastery of the system itself, it is essential that the user be trained with the device at an increasing difficulty and learn to operate it proficiently.
- Ame no Habakiri — This Symphogear has gone through the most changes. In the time between the series prologue and the beginning of the main story, it gained additional armor plates on the shoulders and back, together with longer blades on either ankle, along with a majority of it becoming white. In G, her neck-fabric became smaller and more settled, and a whiter color scheme. During GX, Tsubasa gets a more turquoise color scheme on her outfit and some fabric on her hips are removed, exposing some skin and providing more movement.
- Gungnir — Between the first and second seasons, Hibiki's Gungnir had the pistons used for her punches replaced with much bigger rockets, thus eliminating the need for her to manually pull the pistons back for each attack and giving her a wider array of attacks. She also gains two long ribbons with gems on them, and a small yellow skirt. In GX, the entire gear becomes yellower in color and she loses the fabric on her torso, exposing more of her skin and resembles Kanade more. Her ribbons also become shorter and the skirt becomes more of a skort.
- Ichaival — Chris' gear used to have mostly brown-black and red color scheme, but in G she gets more white and ribbons on her shoes. The headgear grows bigger and covers more of her head as well. She also gains plates on her arms, allowing for crossbows to appear there and allowing more hand-movement. When Chris transforms in GX, the noticeable changes are the red has grown much brighter, and her shoes are now red too and have changed into thigh-high boots.
- Shul Shagana — Between the second and third season, Shirabe's hair-blades grew longer and pointed outwards, providing more defense. She also had the black sections of her gear replaced with white, and her arsenal was enhanced with a pair of razor-bladed yo-yo weapons. The color scheme becomes a brighter, and much lighter pink than before.
- Igalima — Kirika's gear had its black sections became white and the green parts became much lighter. Her helmet and shoulder-blades became green and much glossier, and gained high-heeled boots intend of just heels. Also, she gains a small four-pointed green star on each thigh.