A 1-year panel study of 591 children in fifth grade explored the accumulative effects of the presence and contexts of video game violence on aggression and the antiviolence norm in Japan, on the basis of a comprehensive content analysis of video game violence. The results suggest that contextual effects of violent video games are quite complex, differing with gender, and that contexts are more important than the quantity of violence. Although attractive perpetrators and justification of violence increase aggression for boys, they decrease aggression and strengthen the antiviolence norm for girls, indicating that the direction of effects depend on the players' interpretation of violence. (Contains 4 tables.)