The growing adoption of gameful experiences make their development increasingly complex due to, for example, the number and variety of users, goals, potential mission criticality, and their inherent interdisciplinary nature. This complexity is exasperated by current limitations in theoretical grounding and methodologies to engineer the intended solutions. To help address this complexity, the ICSE 9th International Workshop on Games and Software Engineering (GAS 2025) seeks to highlight the opportunities and challenges involved in emerging trends and issues related to the development of gameful systems (entertainment games, serious games, and gamified applications). The workshop provides a forum to explore issues that crosscut the software engineering and game engineering communities.