Ruri Ohbayashi, a grieving first-year high school student orphaned by a house fire and living with her aunt's family, has her world upended at a "B-Flash" concert. Seized by the band's vocalist, she is pulled through a mirror into the Prussian Moon (or Pulsean Moon). In this realm, Ruri discovers her bloodline descends from royalty, granting her inherited superpowers. Thrust into the heart of a conflict determining this world's fate, she must embrace her destiny to save the Prussian Moon while also fighting to rescue Toru, her lover gravely wounded shielding her during the violent interdimensional transition.