I hope they dont do the mushoku tensei or the reincarnated assassin thing and make the cousin the main love interest...
I'm sure there are more, but that would only prove that it's an ongoing obsession. We aren't in the middle ages anymore, even if these stories are about a similar time period, that doesn't mean you need to go full nobility puritan with them. There are PLENTY of people to choose from other than family members, and if there aren't, MAKE THEM! It's your story, write something other than incest, for the love of all that is decent.