When a hero reaches maximum level, they can be ranked up to increase their limits even further. To do this you need a hefty sum of gold and enhancestones, purple stones that allows heroes to limit break. There are a variety of ways to get enhacestones, but the main method is to venture up the Babel Tower, a mysterious tower that unlocks at profile level fifteen. You will fight against randomized enemies on each floor, but conquering them is worth a lot of enhancestones.