Steel
You come across a gold hill. You think you hit it big! You start digging, only to find out that it is merely a paper-thin layer of gold covering a hill of steel.
Dig out many other spots. Every time, it's just steel under there.
こう
はがね
None
You report your findings about the steel you found to Emperor こういち. He is displeased that it is a hill of steel.
"I suppose I can use this steel, even if it is not a hill of gold," he says. "We will make steel weapons, which we will use to subjugate other nations. The whole world will learn kanji using the WaniKani system!"