After working herself to death as an office employee, Azusa is reincarnated by a goddess as an ageless, undying witch and settles in the highlands for a quiet life. Her routine of hunting slimes in the nearby forest for magic stones to sell quietly stacks experience until, three centuries later, she hits level 99 without noticing. Once word of the Witch of the Highlands spreads, challengers and would-be companions start showing up at her door.