The Executioner and Her Way of Life, Vol. 2 (manga) — Mato Sato

On the train to Garm, the ancient capital where Akari is to be sent home, a terrorist attack and a foe conjured via taboo magic block her and Menou's path. And if that wasn't bad enough, the train is sent careening out of control, headed for an inevitable collision! The only way to stop the impending disaster is for Menou and Akari -- Executioner and her Otherworlder target -- to join forces. But as Menou will soon learn, this is only the beginning of a sinister plot centered around them...