If I had to guess, I'd say the left column is Attack and Defense, the middle column is, no idea, I've been looking to improve one, both, or neither but I don't see any change (Speed, Attack, Exp, IDK), and the right column is Critical Chance and Critical Damage (?). The keys allow you to open a chest before starting, which gives you, again, no idea. And the pink pieces allow you to buy upgrades before starting.