Saijaku Muhai no Bahamut

Undefeated Bahamut Chronicle (最弱無敗の神装機竜, Saijaku Muhai no Bahamut) is a light novel series written by Senri Akatsuki and illustrated by Ayumu Kasuga. A manga adaption written by Senri Akatsuki & Itsuki Watanabe amd illustrated by Fumi Tadauri has been serialized in GA Magazine since Jul 17, 2014. An anime adaption produced by Studio Lerche aired from January 11, 2016, to March 28, 2016.

Plot
Lux, a former prince of an empire named Arcadia that was overthrown via a rebellion five years earlier, accidentally trespasses in a female dormitory's bathing area, sees the kingdom's new princess Lisesharte naked, incurring her wrath. Lisesharte then challenges Lux to a Drag-Ride duel. Drag-Rides are ancient armored mechanical weapons that have been excavated from ruins all around the world. Lux used to be called the strongest Drag-Knight, but now he's known as the "undefeated weakest" Drag-Knight because he will absolutely not attack in battle. After his duel with Lisesharte, Lux ends up attending the female-only academy that trains royals to be Drag-Knights. (via Anime News Network)

Official
Offical Light Novel Site

Offical Manga Site

Offical Anime Site

Other Sources
Wikipedia

MyAnimeList.net (Anime)

MyAnimeList.net (Light Novel)

Anime News Network

Other Wikis
w:c:saijaku-muhai-no-bahamut - 63 pages