It looks like it is
They said it isn't
In the first panel they are biologically twins and kiss on the mouth. Maybe the twin is a reincarnation but it’s definitely physically incest
If you read the full story you'd learn the boy is not human and is in fact a created devil that used two souls to create the shape of a human, and yes their sibling-ness is really weird since you don't know they are not biologically related till much later. Not incest but might as well be....(not physically incest but actually morally incest since they grew up thinking they were siblings which is also gross). Fun times!
It is they are twins
I dont get it. Is it incest or what?