And we keep telling you that the letter only enables STEPcest... Mira and you CAN (if THE PLAYER deliberately decide for it) have the same dad, but never the same mother.
By definition that is
not "stepcest".
Step-siblings have no blood relations to eachother, whilst half-siblings do, therefore incest, and Marcus and Emily weren't married.
Both Mira and the MC are, literally, bastard children whose parents were not married, and Mira and has two half-siblings - Frisha and the MC.
It's what people call relationships between people only shareing partly the same relatives.
Be it by being remarried or one parent haveing more kids with someone else than a kids parent, etc.
An Internet term most commonly said
A combi of Step-mother/-sister/-brother/-father/-daugther/-son and incest... but I gues that's pretty obvious to begin with
People say a lot of retarded and nonsensically ignorant things.
It's really simple.
Woman with child marries man with child. Their children are now step-siblings and they are step-parent to one child each, whilst still parent to their own biological children.
They then go on to have more children together. Those children are now the half-siblings of the original children and have no step-parents or step-siblings at all.