Bullying is widespread in European schools, despite multiple intervention strategies having been proposed over the years. The present study investigates the effects of a novel virtual learning strategy ("FearNot!") to tackle bullying in both UK and German samples. The approach is intended primarily for victims to increase their coping skills and further to heighten empathy and defence of victims by non-involved bystanders. This paper focuses on the defender role. Applying quantitative as well as qualitative methodology, the present study found that "FearNot!" helped non-involved children to become defenders in the German sub-sample while it had no such effect in the UK sub-sample. German "New Defenders" (children who are initially uninvolved but are nominated as defenders by their peers after the intervention period) were found to be significantly more popular at baseline, and to show more cognitive empathy (Theory of Mind) for the virtual victims as compared to permanently non-involved pupils. Moreover, gender interacts with becoming a defender in its effects on affective empathy, with emotional contagion being particularly associated with New Defender status among girls. The findings are discussed in relation to previous research on anti-bullying intervention strategies and cultural differences in bullying prevalence rates and intervention outcomes.