From Wikipedia:
Two idols, Tsubasa Kazanari and Kanade Amō, collectively known as Zwei Wing, battle against an alien race known as Noise using armor known as Symphogear, which uses the power of music to counteract the Noise's destructive capability. However, Kanade sacrifices herself to protect a girl named Hibiki Tachibana, who ends up with a piece of Kanade's Symphogear relic, Gungnir, embedded in her chest. Two years later, Hibiki awakens the power of the Gungnir relic inside her body, gaining the same Symphogear armor that Kanade had. Using the power of song, Hibiki and her fellow Symphogear wielders must fight to protect the innocent and defeat those who would use the Noise for evil.
