The Trip to the Other World was Just for Training!?

Ian Hart was 20 years old and in a rut. He was unemployed and living with his parents. He was suddenly transported to another world one day, one filled with danger, magic, and dungeons. It was in that world that Ian broke his rut. Having played many games and reading novels of the fantasy genre, this new world was like a dream, even with the many dangers. Now a year later he is being brought back to our world, along with his companions he met in his travels. Turns out the other world was dying and our world is next on the list, Ian and the other summoned people are now the best hope the world has at resisting the dungeons that have appeared on the earth.