ERP larp is a live-action role-play game designed to make exposure and response prevention therapy for people who have obsessive compulsive disorder more accessible. Although it is not meant to substitute therapy, it is a self-help guidance that can be applied at home. The research and design combine studies regarding OCD, game design core loops, and larp studies and is an experimental game design. In-depth interviews, quantitative data from the playtester and autobiographic observations are applied to assess its effect on the playtester. The analysis demonstrates that ERP larp is successful in lowering the effect of OCD on the playtester by lowering their anxiety and improving their sense of agency / control. However, the results are not conclusive. It is a pilot study conducted with one playtester and as only two playtest sessions were conducted and data shows that the changes are not substantial. Future research and additional playtests are required to develop and assess the efficacy of ERP larp.