Serious mode for a moment...
I used to have an issue with parent-sibling incest since if the parent had a child with someone he or she fell in love with I dont agree with being infidel with another relationship, incestuous or no.
But then I thought...what if the child was born out of accident? Not accident as in "oops forgot protection" but accident as in it wasn't sex with someone you loved? Doesn't have to be something so severe or dark as rape...maybe you just got super drunk and had a fling with someone one night with a ninth month hangover.
In those sorts of cases, parent-sibling love I'd argue is therefore possible.
Un-serious mode now.
I was hella surprised by this. At first I thought the incest tag was just mistagged for the roleplay. I had to double check the last page to make sure I was right the first time lol