Datte, Watashi wa Freedom! Makoushi Fey, Kodai Bunmei ni Idomimasu

Faye Leonheart is a seventeen-year-old sword-fighting prodigy and the heir apparent to the mightiest warrior clan. After three long years, she finally returns from her sword- training pilgrimage...with a magical machine gun in hand?! Promptly disowned by her family with nothing but her beloved firearm for company, this trigger-happy young lady commits herself to studying ancient technology called overgear. After all, who has time for regrets when freedom calls? The world is full of archaic ruins, and Faye is ready to explore them, full-metal style!

(Source: Yen Press)