Genre Fantasy

Why can't I make my main character a brawler? She was really good with the gauntlets, so it's basically all I used her for. But now, she's reached level 20, but I don't have the option to certify her as a brawler. What's going on? It's available as an option on plenty of the other characters. Are there certain classes she just can't access? Is that random, or will it change with time? Any help would be appreciated.