The paper is the next step in the search for a formal role-playing game (RPG) model. The main contribution of this paper is a system of graphs, which clearly shows the structure of the formal RPG model proposed. With this system, the game world is optimized for easy application of game mechanics using graph rules. In addition, the system of four graphs, such as locations, characters, items and plots graphs, can be useful in the conceptual design phase of computer games because it allows for modifications at the level of component graphs. On the one hand, the holistic model of the game structure fully complies with the proposed formal graph model, on the other hand, its implementation in the Godot engine is performed to prove the concept. The formal definitions introduced in this paper will be illustrated with examples related to the presented case study.