Game with cryptocurrency

I need a top tied blockchain developer, who can develop a mobile app game. The game should include cryptocurrency within it, so that the clients buy new functions with token issued. The tokens should be also used to buy another coins, mostly bitcoin. In other words the cryptocurrency in this game should be interchangeable with bitcoin provided that it pays transaction fee to my game administrator. If you are an expert and read this text, please write "bitcoin and ethereum" in the header of your bid.