While proceeding through the forest and jungle, you'll come across the Nun and Monk that will offer to upgrade your abilities in exchange for Ringsel, red gems that you'll find throughout your travels. The first upgrade with the Nun will require 5 Ringsels (meaning you'll need 4 more after meeting them). Once you've acquired the amount, enter your Inner Realm, head to the right, and you'll be able to upgrade your attack as well as gain the Monk's aid.