As you progress deep into Episode 1 you'll reach the quest
Haddred who is the Chrome Dragon will attack you while you're with Quna
This achievement will unlock upon defeating the Dragon.
There's also an Urgent Quest called
The Grudge of Rampaging Dragons
This quest is to defeat a Chrome Dragon however since there is another Achievement related to finishing Episode 1 to unlock Quna as a partner you'll be doing the story related fight regardless.