Shinju no Nectar

Sakra, the last surviving princess from the fallen kingdom of Adaar, is being hunted down by the Dhala Empire for the power of Ambrosia she possesses, the ability to grant divine strength, but only to a human. With no human companion, she decides to summon one from another world in a desperate attempt to find a marebito, a warrior to protect her, but the man who answers her call isn't quite what she had hoped for. Enter Kai Watari, a perfectly ordinary human from Japan. As a human, he is uniquely capable of being blessed with Sakra's god curse and fighting anyone who stands in her way. However, it quickly becomes apparent that his broad understanding of technology is far more valuable. In this new world, which is slowly industrializing, he knows enough to help technology leap forward.