I finished 8 stages of the quest and I should say: the quest is waaay too hard to provide only 10 keys!
And you @staff say this game is not pay to win?!
Edit: stage 9, one slash attack of a monster (not boss) deals 342 damage to my Lianna - 20 talents + limit break
Edit 2: same stage, a boss deals 800 damage in a slash attack to my Frosth, LB + 20 talents