I Got a Cheat Skill in Another World and Became Unrivaled in the Real World, Too, Vol. 4 (light novel) - Carley Radford, Rein Kuwashima, Miku Miku

A Knight in Shining…Thunderbolt Armor?!After stopping an assassination attempt on King Arnold and Princess Lexia, Yuuya is roped into the hunt for the traitorous Prince Reigar. In the ensuing chaos, a mysterious girl attacks without warning. Her goal? Destroy the world! To have any chance of holding his own against this new foe who is on par with Master Rabbit, Yuuya will have to think fast—as fast as lightning. Hopefully, his quick thinking will be just as useful on Earth, because when Kaori visits his place to study for midterms, she accidentally stumbles upon the door to the other world!