Where does this figure come from? From the wiki of Northern tribes, it states she buries 400,000 northerners at once and then breaks and kills their hero, Numa Seika.
In the manga, I see her kill the hero in Ch. 7 and in Ch. 10 we see Esdeath's 3 henchmen throw tribesmen into a pit to be buried alive. It doesn't directly state northern tribesmen but even if they were northerners, where does this 400,000 number arrive from?