Due to a divine mistake, Takumi Kayano loses his life and is reincarnated. Bestowed with various skills and sent to another world, he finds himself in a dangerous forest teeming with monsters. There, Takumi discovers what seems to be a pair of young twins, a boy and a girl, whom he names Allen and Elena, and takes them under his protection. Astonished by the twins' ability to easily defeat monsters with their martial arts skills, Takumi eventually reaches a town and registers with the adventurer's guild to make a living. Thus begins a leisurely adventurer's life for Takumi as he watches over Allen and Elena's growth.