easy survival in another world

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!!