"Oh, well, this one sibling is conveniently adopted so it's not like it's ~really~ incest if he's in love with his sister."
Well...maybe. There's more than one kind of adoption in Japan which could certainly be influencing the storytelling. You can adopt a kid in the Western sense, you can adopt an orphaned kid through duty (he's a relative's child, he's the child of someone to whom you feel obligated or someone who was in your protection) and that child may or may not be treated as part of the family. There's also adult adoption where the older gay person adopts their younger partner so they can be a family, or adult adoption when a family with no sons adopts their eldest daughter's husband as their son, but he's still married to the daughter despite technically being her brother. So I think there's probably some different concepts about adoption influencing that. No excuse for fucked up crap that women keep having to forgive, though.
no subject
Well...maybe. There's more than one kind of adoption in Japan which could certainly be influencing the storytelling. You can adopt a kid in the Western sense, you can adopt an orphaned kid through duty (he's a relative's child, he's the child of someone to whom you feel obligated or someone who was in your protection) and that child may or may not be treated as part of the family. There's also adult adoption where the older gay person adopts their younger partner so they can be a family, or adult adoption when a family with no sons adopts their eldest daughter's husband as their son, but he's still married to the daughter despite technically being her brother. So I think there's probably some different concepts about adoption influencing that. No excuse for fucked up crap that women keep having to forgive, though.