School bullying is responsible for a large number of child suicides in Japan. Serious games have proved to be effective and highly motivational educational tools capable of increasing awareness, changing behavior, reduce risk factors and even improving protective skills. This paper presents a novel approach of using both participatory design and gameplay to sensitize children (aged 7-12 years old) on bullying victimization. Action research strategy is used with intentions to improve the quality of school life in Japan through the use of a serious game called Shimpai Muyou. What makes it stand out from the rest of the crowd is that the entire intervention was design, developed and evaluated through partnering with children in a school setting. The research is largely qualitative and exploratory in nature, stemmed from interdisciplinary core ideas related to technology, education, psychology and interactive theatre. Findings from both formative and summative evaluations indicated that child-users empathically engaged with the synthetic characters, attributing a range of emotions to their actions e.g., empathy, compassion, sadness, anger etc., tackling ethical dilemmas and bullying situations with confidence. From these results, we can conclude that Shimpai Muyou is a useful and engaging school-based anti-bullying intervention.