Lux Arcadia, once a prince of the fallen Arcadia Empire, works odd jobs at an all-female academy that trains noble women to pilot ancient Drag-Ride war machines. An accidental encounter in the academy's bathing hall draws him into a duel with the new kingdom's princess, Lisesharte Atismata, and though Lux has never lost a Drag-Ride fight, everyone calls him the 'Undefeated Weakest' because he refuses to strike back. Enrolling as a student proper, he's drawn deeper into academy life alongside Krulcifer Einfolk and Yoruka Kirihime as the deposed prince's presence among the nobility draws suspicion.