This article explores the history of marriage laws in Japan, the current legal status of sibling marriages in Japan, cultural attitudes towards them, and the debate over whether or not they should be allowed. It is illegal for siblings to marry each other in Japan due to concerns about genetic defects resulting from interbreeding within families as well as potential psychological damage and social stigma associated with such unions. Cultural attitudes towards sibling marriages vary widely throughout different regions of Japan but generally speaking most people are against allowing them. If allowed, there could potentially be both positive and negative impacts associated with allowing sibling marriages in Japan.