This shouldn't even be a question?? If you don't support it in real life why would you support it in anime, tv shows, or games?? If they are step siblings I can see where you would support it but if they are actually genuinely related no bro 2 reply
It's fiction. In fiction people express their darkest and most controversial ideas. Becuase it's fiction and those characters do not exist and are merely a creation made my ink, I don't see what would be wrong by shipping nonexistent siblings. That doesn't mean you'd ship real life siblings. Unless you're unable to make the distinction between fict...... reply