In a study on several cousinfuckers, 70% of the children were found with to have mental development issues (they were retarded).fun fact: the expected rate of birth defects in the children of first cousins isn't really any higher than that for couples not as closely related.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3904202/
I’m all down for reading these manga and ero doujins, they are harmless. But all of these inane comments saying that irl anti-cousin stems for religion or some type of ignorance, is in itself fucking ignorant. You shouldn’t inbreed because it makes your kids at risk for genetic disorders and deformities. As one fellow above said, touch some grass.