The Last Blacksmith

The Valkyrie, human women who hold the ability to stave off the extinction of the human race with their companions the blacksmiths.
Though the Valkyrie weren't invincible, death was common among them and even more common was the death of their blacksmith. As time went on the replacement rate for Valkyrie was faster than blacksmith until suddenly they all stopped.
For hundreds of years no one was born with the ability of a blacksmith further reducing the human population, until one day a man who was there for his mandatory class revelation in front of everyone is reveled to be a blacksmith.