This is the main armament of the Symphogear.
An Armed Gear is usually equipped with movable and changeable parts (gimmicks). Depending on the user's control limitations and available techniques, it's possible to change its form completely.
The user's visualization of the underlying form of their relic, such as a spear (Gungnir) or a katana (Ame no Habakiri), plays a large part in determining what form the Armed Gear will take.
The current user of Gungnir, Tachibana Hibiki, has been unable to bring a physical form to her Armed Gear. To that extent, her combat abilities have fallen short when compared to Kanade and Tsubasa.
Nothing really new here, though it's interesting that the various techniques they use with their Armed Gear seems dependent upon their ability to will it into a different form. So they don't necessarily have a preset list of attacks, but rather than can come up with their own as needed. This explains why Chris is able to change the type of armaments she has so frequently, at least that's my theory.