Yeah we got a family friend from a distant village who got arranged-married to her cousin and has two kids with him. It's pretty weird to us city folk and makes things awkward if it's even brought up. Eventually you stop bringing it up even in your own brain and just treat them as you would a normal family.
Different country and circumstances, but maybe there are some commonalities with Japan? Those guys have weird little spots in their culture considering how advanced they are as a country. They're supposed to be illegal in South Korea, for example.