The story follows Mercuria, a young woman that doesn't know what to do with her life. After her grandfather's death, amongst her inheritance is a letter in which he asks her to finish what he couldn't, searching for the objects made with the horn of the demon Belzerax, which contain part of his power, and face him. His return is unavoidable, and he'll bring Ragnarock (cool name, huh?), the battle that'll end in humanity's salvation or the beginning of Belzerax's reign.
Each of the band's members are based in different genres and stars, and I want to shown themes of hard work, thirst for power, ego, exploring the world and good vs evil.