More than ten years have passed since a means of transporting individuals from Earth to another world was developed. High school student Kakeru Satomi was taught survival techniques and wisdom by his mountain-dwelling grandfather. Kakeru was sent to another world together with 100 other adventurers of the same age in order to take part in a training program to become an adventurer, but the portal device that linked Earth and the other world vanished right after their transfer. With the way back to Earth blocked, thus began a dangerous life of survival on an uninhabited island in another world.