After Mir was sealed away in the Crescent Chronicle thanks to the efforts of Shurelia and Tastiella De Lu's sacrifice, she continued her actions to destroy mankind by continually sending viruses and making them manifest in the real world through this place to attack the people. Due to this, the humans that had participated in the battle for sealing Mir away, the Apostles of Elemia, established the city of Platina just above the Symphonic Reactor and imposed upon themselves the mission of watching over the Reactor and annihilating any virus that came out from it.