Since this word is made up of a single kanji, it probably uses the kun'yomi reading. You did not learn this reading, so here's a mnemonic to help you:
You take a look at the steel. It's shaped like a person. Turns out you turned that hag into a steel statue. You say, "huh, that's the hag ね?" (はがね). Whoops, sorry hag lady.
How much is the steel armor in the game?