Undefeated Bahamut Chronicle

Lux, a former prince of Arcadia, was once known as the strongest Drag-Knight before a rebellion overthrew the empire five years ago. After trespassing in a female dormitory's bathing area, he's forced into a Drag-Ride duel with Lisesharte, the kingdom's new princess. As the "undefeated weakest" Drag-Knight, Lux has an unusual stance in battle: he won't attack, no matter the circumstances. He ends up attending an all-female academy that trains royals to master the ancient armored mechanical weapons known as Drag-Rides.