The automation of complex negotiations is required to coordinate various AIs. In complex negotiations, the goals of each agent may not be shared because some agents may benefit from not disclosing their own information during negotiation. This uncooperative situation requires an agent to have the ability to infer the intention of the others from the communication, and also to persuade the others through communication. Such negotiation in hidden identity is a pioneering area on negotiation research. In the past, the authors have proposed an AI competition in the Werewolf game in order to research negotiation in hidden identity. To eliminate noise caused by the difficulty of handling natural language, it is necessary to create a model of communication between agents in such a competition. In this paper, we analyze the elements necessary for communication between agents in the Werewolf game and design the protocol between agents based on this analysis.