Akashic Records of Bastard Magic Instructor, Volume 15 (Akashic Records of Bastard Magic Instructor #63-67)

Glenn, his students, and the entire town of Fejite are trapped underneath the Flaming Ark, a flying battleship with the power to burn whole cities to ash. With a seemingly invincible demon at the ship's helm, the odds are stacked against the city's defenders. It'll take everything they've got to stand a chance, and so Glenn makes the tough choice to use a power he'd abandoned long ago, even if it means coming face-to-face with all the trauma of his past.