Since there are several stones out there already, I suggest that you add another type of stone that is specifically purchased with real money and not those that were just accumulated by watching Ad or completing tasks, etc. Only by separating those who purchased will it be easier to directly assist the paying members. I don't think you guys track who have unlocked chapters of the novels by paying for SS or those who just accumulated the SS.
Power stones and Energy stones should also b tracked per users so that it's easier to track the type of novels / author / translator that interests the readers.