Hi! If you click on the gem balance icon, top left of screen (in game) you can choose which bundle to buy. There are several to choose from for a couple of dollars up to over a hundred dollars (depending on your currency). Your game is connected to your play store account, so you either buy a card at the shops and load it to your account or you use a credit card. It depends on how you've set up your google play store account. Hope that helps!
I don't want to sound ignorant, but where do I find details regading buying energy in Castle Story? What forms of payment? If you play on android, can you use an Apple gift card (if that is even a form of payment)?
