Narrative-based serious games are accessible, engaging technologies that connect users’ lived experiences to pedagogy. Despite having patient-centered goals, most narrative-based serious games are not designed alongside patients and communities, limiting their likelihood of acceptance, uptake, and impact. Literature reveals that many serious games intended for patients merely evaluate efficacy with end-users after game deployment and with a lack of consistent participatory design. This work aims to describe a patient-centered participatory approach to game development to teach self-advocacy skills to patients newly diagnosed with cancer. First, characters were developed based on panels that included patient advocates, cancer survivors, clinicians, and researchers. Second, storyline development created realistic story arcs, decision-points, and consequences based on qualitative interviews with patients, patient advocates, and cancer survivors. Third, game evaluation metrics (e.g., 1st vs. 3rd person perspective, game fail states that incentivize replaying the game, and provision of implicit or explicit feedback) were developed based on accessibility, usability, and patient preferences. Based on patients’ insights, we implemented changes accordingly to maximize the game’s efficacy and collected qualitative data on patients’ assessment of the game’s accessibility, relevance, and impact. During initial game development, patient and advocate feedback built relatable characters with a particular focus on providing sensitive information (e.g., palliative care) and inclusive storylines (e.g., diverse family situations). Following a prototype, patients and advocates suggested refinements to characters and additional storylines, including common and/or distressing experiences related to pain management, family dynamics, financial struggles, and disrespect from healthcare providers. Participants in a randomized trial of the game (N=34) found the scenarios relevant and realistic. Patients reported increased comfort speaking up, seeking support, and interacting with their families and healthcare team after playing the game. Our process demonstrates the essential role patients can inhabit in the development of narrative serious games, particularly in how patient input permeated every aspect of Strong Together's development, from initial design to evaluation. Such integration allows for adjustments to address patient concerns and refine patient-relevant metrics.