I'm part of a group of 3 (relatively new) people playing an RPG called Challenger. All three of us are interested in being GM, so we've been rotating; all of our adventures occur in the same universe, but they aren't necessarily connected, so one runs a small adventure in one sitting, then the next runs an unrelated adventure the next week, and so on. However, after playing for a while and getting used to the system, we realized that we were extremely overpowered (really strong loot, and strength in general; one of our players knocked down a castle with one non-critical hit) and started a new universe with more-balanced characters and loot and stuff.
The problem, though, is that one of our players refuses to let go of his old character. He fought to give his character items from before (which we had decided were too powerful for our level), and constantly references and revisits the past universe. He continues to do this despite compromises--we let him make a similar character, and tried to nerf some of his weapons. We all enjoy doing this, and since it's such a small group we can't afford for him to leave the group; what can we do?