My Instant Death Ability Is So Overpowered, No One in This Other World Stands a Chance Against Me! -AO-, Vol. 4 (manga)  (English, Paperback, Naruse Chisato)

With the events of Hanabusa behind them,Yogiri and Tomochika's journey to the capital has brought them deep into the wilderness of the Garula Canyon, where they meet an enigmatic man known only as the Swordmaster. In hopes of finding any information that might help them get home, the two reluctantly decide to participate in the trial unfolding there: a selection process for those wishing to become Knights of the Divine King. But when Yogiri slips up and accidentally uses his power to kill someone central to the history of the world, their objective quickly changes to escaping the tower where the trial is being held before anyone realizes what he's done.