You know, I understand that at some point you could still have gotten off this ship, and t...

You know, I understand that at some point you could still have gotten off this ship, and that it was by our own volition, that we let ourselves be carried across the psychological pseudo incest ocean of this manga, but I still have to ask: Can't they drop the onii-chan now that they're registered spouses?? At least in public??? Imagine you're the poor office worker happily giving another couple the news they were waiting for and oh, good curious, they have the same last name! There must be a funny story behind that haha, and as you hand them the paper, the new wife starts scolding her ducking onii-chan???