Board Thread:Questions and Answers/@comment-85.244.16.235-20160109224217/@comment-26178479-20160312232808

What they said. Beating story missions on each difficulty for the first time drops Z stones, all of the event missions will drop some number of Z stones based on certain conditions, and there's a few you can get from completing missions. Oh, and the world tournament has Z stone prizes, whenever that's in town.