My Instant Death Ability is Overpowered

The Sage who brought Yogiri Takatou's school bus to another planet demonstrates to the children how terrible both the world and she are by murdering the adults for trivial reasons and instructing them to become sages in order to battle demons. She leaves the others to perish, taking only the skilled. Yogiri seeks to return with his classmate Tomochika Dannora, but Tomochika becomes uneasy due to Yogiri's indifference to the strangeness. Yogiri is actually not your typical child; he has the ability to willfully kill everything.