Devising a system requirements specification is a challenging task. Even after several decades of system development research, specifications for large-scale, widely-used systems remain difficult. In this paper, we suggest a first step toward a requirements specification through a stakeholder involvement approach with game elements. We report preliminary findings from a practice case in which our methods are applied to the requirement specification phase of a project management system. The analysis showed that our game approach fostered innovative idea generation and captured implicit user expectations, and as a result provided a list of requirements from other perspectives than those of conventional specification analysis. The granularities of extracted system requirements need to be refined and transferred to detailed requirements for developers to use, however, our results imply that our stakeholder involvement method with game elements can be effectively utilized as a first step towards requirement specification.