The guy in the world of giantesses

This will be about a guy who fell into the world of a giantesses against his will. This world is very similar to an ordinary human one. However, all technologies of that world are associated with magic. Every giantess can make a magic. But each giant girl needs an individual magic amplifier for the full use of her abilities. And this magical amplifier is a specially selected man from the human world. - The main character of the novel is the guy who got into the world of giantesses instead of his friend by mistake. The guy's task is to return to his world.​