This achievement is extremely deceiving. Most people assume that all you have to do is get every character to level 9 and youll get the achievement. Thats not true. What you really have to do is get every character to level 9 than re-beat the entire game (redo every single mission) with all 7 characters at level 9. I know its dumb but thats how it works. Some people think its a glitch but it isnt.
Where to level for each character:
Inphyy: Fort Wyandeek (explore all areas branching off)
Aspharr: Fort Wyandeek (explore all areas branching off)
Myifee: Pholya Flatlands (when you have to stop the goblins going across the bridge which is the area with the block rate, dont let the block rate hit 100.. just keep waiting and waiting until you get bored than finish it off)
Dwingvatt: Bastide of Varrgandd (make sure to kill as many guys as you can)
Tyurru: Pholya Flatlands
Klarrann: Pholya Flatlands (not a lot of kills but the orbs received are A LOT and it will save a lot of time instead of Fort Wyandeek)
Vigk Vagk: Pholya Flatlands (there is 4 bosses in this and you gain a lot of experience off them. Dont use Bastide of Varrgandd even though you receive more orbs, your experience doesnt add because the bosses drop 3 bonuses XP tombs and you get 12 in total. If you want to save time do Pholya Flatlands).