いとこ婚
In some cultures and communities, cousin marriages are considered ideal and are actively encouraged and expected; in others, they are seen as incestuous and are subject to social stigma and taboo. Cousin marriage was historically practised by indigenous cultures in Australia, North America, South America, and Polynesia. Different religions have ranged from prohibiting up to sixth cousins from marrying (some forms of Hinduism and Catholicism) to freely allowing first cousin marriage (Protestantism, Islam and Judaism).