In the future humanity is plauged by these obnoxious looking blob things called the noise. They are a real problem seeing as how human weapons have no effect on them. Plus if you get touched, you die. Well I won't say none of our weapons have no effect. Apparently in the past we managed to create some super special relics that give humans the power to kill noise. However, these relics are only compatible with certain people, and only work via singing.

Well lucky for Hibiki, I guess, during a concert she attended there was a noise attack. After lots of explosions and death, oddly she is not dead, a chunk of a relic to summon Symphogear was embedded in her chest. Then later on she managed to activate it. Now she has been thrown into the struggle with the noise. You know plus continuing to live her happy go lucky normal life with her potentially lesbian friend.