Fates!

The game where your primary romance options are your adopted siblings who aren't blood related; your long lost siblings you've never met who insist they're blood related to you but actually aren't; or one hot opera lady who won't tell you that she's the one you actually are related to until after you marry her!

All the weird family incest going on in this game really reveals the writer's perspective.
Namely that they don't actually know what it's like to have a sibling and that apparently it's only an issue/awkward if it's blood-related.